fix: upgrade golangci-lint-action to v7 for golangci-lint v2 support

v6 doesn't support golangci-lint v2 - must use v7.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: stubbi

.github/workflows/ci.yaml

@@ -22,10 +22,9 @@ jobs:
           go-version: ${{ env.GO_VERSION }}
 
       - name: golangci-lint
-        uses: golangci/golangci-lint-action@v6
+        uses: golangci/golangci-lint-action@v7
         with:
           version: v2.1.0
-          install-mode: binary
           args: --timeout=5m
 
   reconcile-guard: