ci: skip Code Coverage job when CODECOV_TOKEN isn't available

The Upload step in codecov.yml has `fail_ci_if_error: true`, so when
the workflow runs on a fork (or anywhere else without
`secrets.CODECOV_TOKEN`) the upload returns:

  Token required - not valid tokenless upload
  ==> Failed to create-commit

…and the whole job goes red even though the test suite passed.

Gate the entire job on `secrets.CODECOV_TOKEN != ''` so forks skip
both the test run and the upload — running unit tests just to throw
away the coverage report is wasted CI time. Anyone who actually wants
the coverage can opt in by configuring the secret on their fork.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Signed-off-by: Arthur Schreiber <arthur@planetscale.com>
(cherry picked from commit dea0555)

Author: arthurschreiber

.github/workflows/codecov.yml

@@ -16,6 +16,11 @@ permissions: read-all
 jobs:
   test:
     name: Code Coverage
+    # Skip the whole job when no CODECOV_TOKEN is available — without one the
+    # final upload step fails ("Token required - not valid tokenless upload"),
+    # so running the test suite just to throw the report away is wasted work.
+    # Forks that want coverage can opt in by configuring CODECOV_TOKEN.
+    if: ${{ secrets.CODECOV_TOKEN != '' }}
     runs-on: ${{ github.repository == 'vitessio/vitess' && 'gh-hosted-runners-16cores-1-24.04' || 'ubuntu-24.04' }}
 
     steps: