Run operator E2E on one Kubernetes version per PR (#6540)

Every pull request update runs the operator E2E suite against three
kind node versions, about 20 large-runner minutes per run, while
cross-version compatibility almost never breaks within a single PR.

Run only the newest version on pull_request events. Pushes to main
and manual dispatches keep the full matrix, so a version-specific
regression still surfaces on main within one CI cycle.

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

Author: rdimitrov

.github/workflows/operator-ci.yml

@@ -160,14 +160,19 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
+        # Pull requests run against the newest Kubernetes version only; pushes
+        # to main and manual dispatches run the full set. Cross-version
+        # compatibility rarely breaks within a single PR, and the full matrix
+        # still runs on every merge, so a regression surfaces on main within
+        # one CI cycle instead of costing three E2E runs on every PR update.
+        #
         # Before someone says it, yes we could just put the number here and not the full image name,
         # but we want to make sure renovate bumps the versions when new ones are released. Doing that with
-        # just the number is a bit more difficult and i like simple things.
-        version: [
-          "kindest/node:v1.33.7",
-          "kindest/node:v1.34.3",
-          "kindest/node:v1.35.1"
-        ]
+        # just the number is a bit more difficult and i like simple things. The newest version appears in
+        # both lists so renovate keeps them in step.
+        version: ${{ github.event_name == 'pull_request'
+          && fromJSON('["kindest/node:v1.35.1"]')
+          || fromJSON('["kindest/node:v1.33.7", "kindest/node:v1.34.3", "kindest/node:v1.35.1"]') }}
 
     steps:
     - name: Checkout code