workflows: don't re-run GitHub Actions CI on edited event

This event is only triggered if the PR body or title is updated or if
the base branch is updated. A base branch is typically not updated and
we don't rebase anyway, so that would not affect the result of the CI
job anyway. So it seems this event can be skipped and we can save on
CI re-runs.

Epic: CRDB-8308
Release note: None

.github/workflows/github-actions-essential-ci.yml

@@ -1,7 +1,7 @@
 name: GitHub Actions Essential CI
 on:
   pull_request:
-    types: [ opened, reopened, synchronize, edited ]
+    types: [ opened, reopened, synchronize ]
     branches:
       - 'master'
       - 'release-*'