dri-pkgconfig-stub: hardcode version

pkgs/by-name/dr/dri-pkgconfig-stub/package.nix

···
 writeTextFile {
   name = "dri-pkgconfig-stub";
 
+  # Version intentionally hardcoded to avoid rebuilds on Mesa updates.
+  # If anything ever requires a newer version, this can simply be bumped manually.
   text = ''
     dridriverdir=${mesa.driverLink}/lib/dri
 
     Name: dri
-    Version: ${mesa.version}
+    Version: 25.0
     Description: Nixpkgs graphics driver path stub
   '';