feat: add environment variables for Go caching in CI workflow

.gitea/workflows/ci.yaml

@@ -10,6 +10,9 @@ on:
 env:
   REGISTRY: gitea.nik4nao.com
   IMAGE_PREFIX: gitea.nik4nao.com/nik
+  GOPATH: /tmp/go
+  GOMODCACHE: /tmp/go/pkg/mod
+  GOCACHE: /tmp/go-build
 
 jobs:
   test:
@@ -17,6 +20,9 @@ jobs:
     steps:
       - uses: actions/checkout@v6
 
+      - name: prepare go cache dirs
+        run: mkdir -p "$GOMODCACHE" "$GOCACHE"
+
       - uses: actions/setup-go@v6
         with:
           go-version-file: go.work