Update codecov-action from v3 to v4 (#1839)

We need to specify the token due to rate limiting of their global
upload token.

We also want the workflow to fail if we can't upload the coverage
report for any reason. Otherwise, it is too easy to overlook the
absence of coverage data.

.github/workflows/run-tests.yml

@@ -66,9 +66,12 @@ jobs:
         run: composer phpunit
 
       - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v4
         with:
           files: test/coverage/clover.xml
+          token: ${{ secrets.CODECOV_TOKEN }}
+          fail_ci_if_error: true
+          verbose: true
 
   phpstan:
     name: PHPStan