chore: remove requiring fetch (#5440)

We should just magically get it... https://github.com/danmichaelo/github-script/blob/da8818015eb5c3d01f8ad6db6bd8e3a2b460c71c/README.md

.github/scripts/close-invalid-link.cjs

@@ -12,8 +12,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-const fetch = require('node-fetch');
-
 async function closeIssue() {
     await github.rest.issues.update({
         owner: owner,