try setting group correctly

.github/workflows/_run_tests.yml

@@ -150,7 +150,6 @@ jobs:
           CI_NODE_INDEX: ${{ strategy.job-index }}
           PARALLEL_TESTS_RECORD_RUNTIME: true
           MINITEST_JUNIT_REPORTER: yes
-
         # TODO: Eventually we want to be able to do this by runtime, but how do we bootstrap that file?
         # This option is used to feed in runtime info from previous runs.
         # --runtime-log tmp/old_parallel_runtime.log \
@@ -159,7 +158,7 @@ jobs:
         run: |
           bundle exec parallel_test test \
           -n ${{ strategy.job-total }} \
-          --only-group ${{ strategy.job-index }} \
+          --only-group ${{ strategy.job-index + 1 }} \
           --serialize-stdout \
           --group-by filesize \
           --combine-stderr \