Bump codecov/codecov-action from 3 to 4 (#1039)

Author: dependabot[bot]

.github/workflows/codecov.yml

@@ -1,4 +1,3 @@
-# TODO: This CI job hangs as of April 2023
 name: Run codecov
 
 on:
@@ -32,7 +31,9 @@ jobs:
         run: |
           pytest --cov=./slack_bolt/ --cov-report=xml
       - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v4
         with:
           fail_ci_if_error: true
           verbose: true
+        env:
+          CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}