Fix CI: install golangci-lint v2.5.0 and use GOPATH

- Pin to v2.5.0 to match local version
- Add version check to verify installation
- Use $(go env GOPATH)/bin/golangci-lint for explicit path
- Add coverage.out to .gitignore

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: ndbroadbent

.github/workflows/test.yml

@@ -61,8 +61,11 @@ jobs:
     - name: Install golangci-lint
       run: go install github.com/golangci/golangci-lint/cmd/[email protected]
 
+    - name: Verify golangci-lint installation
+      run: $(go env GOPATH)/bin/golangci-lint version
+
     - name: Verify golangci-lint config
-      run: golangci-lint config verify
+      run: $(go env GOPATH)/bin/golangci-lint config verify
 
     - name: Run golangci-lint
-      run: golangci-lint run --timeout=5m ./...
+      run: $(go env GOPATH)/bin/golangci-lint run --timeout=5m ./...