ci: replace golangci-lint with go vet

golangci-lint v2 install via 'go install' is too heavy for CI
(compiles from source, needs lots of memory and time).
Use go vet as lightweight alternative for now.

.gitea/workflows/ci.yml

@@ -38,10 +38,8 @@ jobs:
             exit 1
           fi
 
-      - name: Run lint
-        run: |
-          go install github.com/golangci/golangci-lint/v2/cmd/golangci-lint@latest
-          golangci-lint run ./...
+      - name: Run vet
+        run: go vet ./...
 
   test:
     name: Test