ci: update mlugg/setup-zig

Author: kassane

.github/workflows/zigbuild.yml

@@ -17,7 +17,7 @@ jobs:
         with:
           submodules: recursive
           fetch-depth: 0
-      - uses: mlugg/setup-zig@v1
+      - uses: mlugg/setup-zig@v2
 
       - name: Install LLVM (Linux)
         if: startsWith(matrix.runs-on, 'ubuntu')