fix: enable Go module cache in CI workflow

- Add cache: true to actions/setup-go@v5 so modules persist between steps
- Fixes "missing go.sum entry" error on go vet step

.gitea/workflows/ci.yml

@@ -15,6 +15,7 @@ jobs:
       - uses: actions/setup-go@v5
         with:
           go-version: "1.25"
+          cache: true
 
       - name: go vet
         run: go vet ./...
@@ -37,6 +38,7 @@ jobs:
       - uses: actions/setup-go@v5
         with:
           go-version: "1.25"
+          cache: true
 
       - name: Run tests
         run: go test ./... -v -race -cover
@@ -50,6 +52,7 @@ jobs:
       - uses: actions/setup-go@v5
         with:
           go-version: "1.25"
+          cache: true
 
       - name: Build binary
         run: go build -o mrixscraft-server ./cmd/server