build: relax required go version for local development

.forgejo/workflows-composite/setup-env/action.yaml

@@ -13,3 +13,13 @@ runs:
     - uses: https://codeberg.org/fnetx/setup-cache-go@4b50dd28b1068fa06d433c5fabed3f6f4d4ccddf
       with:
         username: forgejo
+
+    - name: validate go version
+      run: |
+        set -ex
+        toolchain=$(grep -oP '(?<=toolchain ).+' go.mod)
+        version=$(go version | cut -d' ' -f3)
+        if [ "$toolchain" != "$version" ]; then
+          echo "go version mismatch: $toolchain <> $version"
+          exit 1
+        fi