feature: use macos-26-intel runner for macos-x64 build

Author: cowwoc

.cat/issues/v2/v2.1/build-git-filter-repo-ci/index.json

@@ -4,4 +4,4 @@
   "dependencies" : [ ],
   "blocks" : [ "2.1-replace-bfg-with-git-filter-repo" ],
   "targetBranch" : "v2.1"
-}
+}

.github/workflows/build-git-filter-repo.yml

@@ -22,7 +22,7 @@ jobs:
             platform: linux-x64
           - os: ubuntu-24.04-arm
             platform: linux-aarch64
-          - os: macos-12
+          - os: macos-26-intel
             platform: macos-x64
           - os: macos-latest
             platform: macos-aarch64