specify mesa-git-unstable to specific rev rather than main

flake.lock

@@ -467,11 +467,11 @@
     },
     "nixpkgs_3": {
       "locked": {
-        "lastModified": 1773646010,
+        "lastModified": 1775036866,
-        "narHash": "sha256-iYrs97hS7p5u4lQzuNWzuALGIOdkPXvjz7bviiBjUu8=",
+        "narHash": "sha256-ZojAnPuCdy657PbTq5V0Y+AHKhZAIwSIT2cb8UgAz/U=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "5b2c2d84341b2afb5647081c1386a80d7a8d8605",
+        "rev": "6201e203d09599479a3b3450ed24fa81537ebc4e",
         "type": "github"
       },
       "original": {

overlays/mesa-gcc/default.nix

@@ -2,13 +2,13 @@
 
 final: prev: {
   mesa = (prev.mesa.overrideAttrs (old: rec {
-    version = "git-unstable-2026-03-22";
+    version = "git-unstable-2026-04-02";
     src = prev.fetchFromGitLab {
       domain = "gitlab.freedesktop.org";
       owner = "mesa";
       repo = "mesa";
-      rev = "main";
+      rev = "72e9f9a760a5dd81a74497f1daef054af1b6b827";
-      hash = "sha256-IoLD9ODAU8sMqnPeDXdPhU3S1fr/UNnmuR3CpZC99Rs=";
+      hash = "sha256-81V5RdLSLYeGJ/wh5H8L6vq+QdR6yMkJxDV+6Yf5FPk=";
     };
     patches = [];
     buildInputs = old.buildInputs ++ (with prev.llvmPackages_21; [