ci: remove --ast-check from zig format

This works around ziglang/zig#22078 (the ast-check behavior changed
since the last successful CI run). Since we build as part of the job,
this check isn't really necessary anyway, though it certainly is
lighter-weight than trying to compile.

.github/workflows/ci.yaml

@@ -33,7 +33,7 @@ jobs:
 
       - if: ${{ matrix.check-format }}
         name: Check Formatting
-        run: zig fmt --ast-check --check .
+        run: zig fmt --check .
 
       - name: Build
         run: zig build ${{ matrix.build-options }} --summary all