This should fix that

diff --git a/pkgs/development/libraries/gstreamer/ges/default.nix b/pkgs/development/libraries/gstreamer/ges/default.nix
index 2e2a9fdae3fa..5ceada67a73f 100644
--- a/pkgs/development/libraries/gstreamer/ges/default.nix
+++ b/pkgs/development/libraries/gstreamer/ges/default.nix
@@ -10,6 +10,7 @@
   gst-plugins-base,
   gst-plugins-bad,
   gst-devtools,
+  gstreamer,
   libxml2,
   flex,
   gettext,
@@ -43,6 +44,7 @@ stdenv.mkDerivation (finalAttrs: {
     gobject-introspection
     python3
     flex
+    gstreamer # for gst-tester-1.0
   ]
   ++ lib.optionals enableDocumentation [
     hotdoc

I'm still building deps

warning: Git tree '/home/quadradical/.config/nixos' is dirty
error: builder for '/nix/store/n4a2w5m6d37skfvcy2lgl4m6pdbwr89y-glycin-loaders-aarch64-unknown-linux-gnu-1.2.3.drv' failed with exit code 1;
       last 25 log lines:
       >    Compiling toml_datetime v0.6.8
       >    Compiling fastrand v2.3.0
       > error: linker `cc` not found
       >   |
       >   = note: No such file or directory (os error 2)
       >
       >    Compiling static_assertions v1.1.0
       > error: could not compile `proc-macro2` (build script) due to 1 previous error
       > warning: build failed, waiting for other jobs to finish...
       > error: could not compile `crossbeam-utils` (build script) due to 1 previous error
       > error: could not compile `serde` (build script) due to 1 previous error
       > error: could not compile `libc` (build script) due to 1 previous error
       > [1/12] Merging translations for loaders/glycin-jxl.conf
       > /nix/store/m705ap2d06cz67bl8xssz33rl9axy3pm-gettext-0.25.1/bin/msgfmt: ../loaders/../po/LINGUAS does not exist
       > [2/12] Merging translations for loaders/glycin-svg.conf
       > /nix/store/m705ap2d06cz67bl8xssz33rl9axy3pm-gettext-0.25.1/bin/msgfmt: ../loaders/../po/LINGUAS does not exist
       > [3/12] Merging translations for loaders/glycin-image-rs.conf
       > /nix/store/m705ap2d06cz67bl8xssz33rl9axy3pm-gettext-0.25.1/bin/msgfmt: ../loaders/../po/LINGUAS does not exist
       > loaders/tmp-glycin-image-rs:27:0: warning: invalid non-blank line
       > loaders/tmp-glycin-image-rs:31:0: warning: invalid non-blank line
       > [4/12] Merging translations for loaders/glycin-heif.conf
       > /nix/store/m705ap2d06cz67bl8xssz33rl9axy3pm-gettext-0.25.1/bin/msgfmt: ../loaders/../po/LINGUAS does not exist
       > FAILED: loaders/glycin-heif-bin
       > env CARGO_HOME=/build/glycin-1.2.3/build/cargo-home LOCALEDIR=/nix/store/cdpamqr3bgswbjkn0bbz4ah259rif5nm-glycin-loaders-aarch64-unknown-linux-gnu-1.2.3/share/locale GIT_DESCRIBE= /nix/store/as0xa9521nz18lgw9a5q3r3x5r4b15pz-aarch64-unknown-linux-gnu-cargo-1.88.0/bin/cargo build --target-dir /build/glycin-1.2.3/build/cargo-target --profile release --manifest-path /build/glycin-1.2.3/Cargo.toml --package glycin-heif
       > ninja: build stopped: subcommand failed.
       For full logs, run 'nix log /nix/store/n4a2w5m6d37skfvcy2lgl4m6pdbwr89y-glycin-loaders-aarch64-unknown-linux-gnu-1.2.3.drv'.
error: 1 dependencies of derivation '/nix/store/g62g4z53fpykmzbkhwxr623smj7y62ky-loupe-aarch64-unknown-linux-gnu-48.1.drv' failed to build
error: 1 dependencies of derivation '/nix/store/jr2bvv6ypxdk1kiq81y8g7vckfrspi99-snapshot-aarch64-unknown-linux-gnu-48.0.1.drv' failed to build
error: 1 dependencies of derivation '/nix/store/grshilj0mrln0ihslfn9zws30a7nnkdg-loupe-aarch64-unknown-linux-gnu-48.1_fish-completions.drv' failed to build
error (ignored): error: cannot unlink 'deps' in directory '/nix/var/nix/builds/nix-build-librewolf-unwrapped-aarch64-unknown-linux-gnu-141.0.3-1.drv-1/firefox-141.0.3/objdir/release': Directory not empty
error: 1 dependencies of derivation '/nix/store/pcb6i896ym3dv7a5lzj847584hlzvavs-man-paths.drv' failed to build
error: 1 dependencies of derivation '/nix/store/d1r8gx1469b5djkyygnr4k5a0fz9fci2-system-path.drv' failed to build
error (ignored): error: cannot unlink 'build' in directory '/nix/var/nix/builds/nix-build-gjs-aarch64-unknown-linux-gnu-1.84.2.drv-0/gjs-1.84.2': Directory not empty
error: 1 dependencies of derivation '/nix/store/ldin4dvw5zark6rp4wzwnh5j03y4671v-etc.drv' failed to build
error: 1 dependencies of derivation '/nix/store/cwj7lw5l8707vw9dg4f3igf1lgmgg5s1-nixos-system-quadphone-25.11.20250812.005433b.drv' failed to build
error: 1 dependencies of derivation '/nix/store/l0v9snvnsyk0m7vy4jmd5injs4sp74s3-image.drv' failed to build

        postPatch = lib.optionalString (super.stdenv.buildPlatform != super.stdenv.hostPlatform) ''
          substituteInPlace meson.build \
            --replace-fail "cargo_target_dir / rust_target / loader," "'${super.stdenv.hostPlatform.rust.cargoShortTarget}' / cargo_target_dir / rust_target / loader,"
        '';