ci: replace codecov upload with coverage summary display

Remove the Codecov action for uploading coverage reports and instead add a step to display a summary of test coverage in the CI output.

.gitea/workflows/ci.yml

@@ -36,11 +36,9 @@ jobs:
         run: |
             go test -v -race -coverprofile=coverage.out ./...
 
-      - name: Upload coverage
-        uses: codecov/codecov-action@v4
-        with:
-          file: ./coverage.out
-          fail_ci_if_error: false
+      - name: Display coverage summary
+        run: |
+          go tool cover -func=coverage.out | tail -1
 
   lint:
     name: Lint