CI(trigger-e2e-tests): fix checking for successful image pushes (#10803)

## Problem
https://github.com/neondatabase/neon/pull/10613 changed how images are
pushed, and therefore also how we have to wait for images to be pushed
in `trigger-e2e-tests`. The `trigger-e2e-tests` workflow is triggered in
three different ways:
- When a pull request is pushed to that is already ready to review, here
we call the workflow from `build_and_test`
- When a pull request is marked ready for review, then the workflow is
triggered directly
- When a push to `main` or `release(-.*)?` triggers `build_and_test` and
that indirectly calls `trigger-e2e-tests`.

The second of these paths had a bug, which was not tested in the PR,
because this path being different wasn't clear to me.

## Summary of changes
Fix the jq statement that caused the bug.

.github/workflows/trigger-e2e-tests.yml

@@ -88,7 +88,7 @@ jobs:
           BUILD_AND_TEST_RUN_ID=${TAG}
           while true; do
             gh run --repo ${GITHUB_REPOSITORY} view ${BUILD_AND_TEST_RUN_ID} --json jobs --jq '[.jobs[] | select((.name | startswith("push-neon-image-dev")) or (.name | startswith("push-compute-image-dev"))) | {"name": .name, "conclusion": .conclusion, "url": .url}]' > jobs.json
-            if [ $(jq '[.[] | select(.conclusion == "success")]' jobs.json) -eq 2 ]; then
+            if [ $(jq '[.[] | select(.conclusion == "success")] | length' jobs.json) -eq 2 ]; then
               break
             fi
             jq -c '.[]' jobs.json | while read -r job; do