[fix][ci] Update GraalVM setup action to ASF-approved version

[lhotari]

Motivation

Pulsar CI fails before starting any jobs because ASF no longer permits the pinned graalvm/setup-graalvm v1.5.4 commit. This blocks unrelated changes, including run 34751336550 and run 34770940645.

Modifications

Update graalvm/setup-graalvm to v1.6.6, pinned to 0426e2e191540e8514dff98dc52a5f5146a2a276, the latest version in ASF's approved actions list. Keep the existing GraalVM distribution and Java version settings.

Verifying this change

• Make sure that the change passes the CI checks.

This change updates a CI action pin without adding tests.

• Verified the SHA against the ASF allowlist and the upstream v1.6.6 tag, and checked that the configured inputs are supported.
• git diff --check passes.
• actionlint -shellcheck='' reports the same six existing matrix-property errors before and after this change, with no new diagnostics.
• ./gradlew spotlessCheck checkstyleMain checkstyleTest passes.

Does this pull request potentially affect one of the following parts:

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Only the CI GraalVM setup action is upgraded.

[lhotari]

Follow-up: #26572 adds the ASF action allowlist check to the CI preconditions. Besides failing CI when scanned action refs are not approved, it emits non-failing warnings for approved pins expiring within 30 days, giving us advance notice to update them before they cause startup failures.