ci: Fix duplicated/failed eval jobs (#33453)

I think this should fix the CI issues with Eval jobs:

1. Duplicated workflows because `synchronize` / `opened` were triggering
distinct runs. This caused failed job entries because the duplicated
workflows had a shared concurrency group and so one would pre-empt the
other.

3. Removes the no-op job, introduced as an attempted workaround in
   https://github.com/zed-industries/zed/pull/29420.

These should correctly show as "Skipped" now:

| Before | After |
| - | - |
| <img width="359" alt="Screenshot 2025-06-26 at 9 57 04"
src="https://github.com/user-attachments/assets/6ddd4f46-27c7-4d82-98ba-0f1166fc55e7"
/> | <img width="355" alt="Screenshot 2025-06-26 at 10 09 54"
src="https://github.com/user-attachments/assets/5faade2c-f17c-447a-9af9-6396f9e53016"
/> |

Release Notes:

- N/A

.github/workflows/eval.yml

@@ -7,7 +7,7 @@ on:
   pull_request:
     branches:
       - "**"
-    types: [opened, synchronize, reopened, labeled]
+    types: [synchronize, reopened, labeled]
 
   workflow_dispatch:
 
@@ -25,16 +25,6 @@ env:
   ZED_EVAL_TELEMETRY: 1
 
 jobs:
-  # This is a no-op job that we run to prevent GitHub from marking the workflow
-  # as failed for PRs that don't have the `run-eval` label.
-  noop:
-    name: No-op
-    runs-on: ubuntu-latest
-    if: github.repository_owner == 'zed-industries'
-    steps:
-      - name: No-op
-        run: echo "Nothing to do"
-
   run_eval:
     timeout-minutes: 60
     name: Run Agent Eval