fix: add go mod download before go vet and tests

- Explicitly run go mod download so modules are available for go vet
- Remove cache: true (unnecessary now that modules are explicitly fetched)

.gitea/workflows/ci.yml

@@ -15,7 +15,9 @@ jobs:
       - uses: actions/setup-go@v5
         with:
           go-version: "1.25"
-          cache: true
+
+      - name: Download Go modules
+        run: go mod download
 
       - name: go vet
         run: go vet ./...
@@ -38,7 +40,9 @@ jobs:
       - uses: actions/setup-go@v5
         with:
           go-version: "1.25"
-          cache: true
+
+      - name: Download Go modules
+        run: go mod download
 
       - name: Run tests
         run: go test ./... -v -race -cover