ci: revert e2e-k3d-kuttl Go pin to stable on REL_5_8

The setup-go pin to 1.25.x in the e2e-k3d-kuttl job, combined with
GOTOOLCHAIN=local in CI, prevented Go from auto-upgrading to 1.26 when
go run-ing kuttl@latest. Recent kuttl releases require Go >= 1.26
(testDeps.ModulePath, etc.), causing both v1.30 and v1.34 e2e jobs to
fail when downloading and building the kubectl-kuttl binary.

Switch the job back to go-version: stable so the runner installs the
current toolchain, matching what we already do on main (PR #4488).

The operator binary itself is built inside Docker against the project's
go directive (1.25.0), so this only affects the host toolchain used to
fetch and run kuttl from source.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: ValClarkson

.github/workflows/test.yaml

@@ -93,7 +93,7 @@ jobs:
     steps:
       - uses: actions/checkout@v6
       - uses: actions/setup-go@v6
-        with: { go-version: '1.25.x' } # TODO: revert to stable when kuttl supports Go 1.26 (missing testDeps.ModulePath)
+        with: { go-version: stable }
 
       - name: Start k3s
         uses: ./.github/actions/k3d