[CI] Pin actions/checkout in dependabot

The latest version of actions/checkout bumps its nodejs dependency to
v20, which requires a newer glibc version than is available in the
ASWF CY22 Docker image.

Ultimately we aim to use GitHub release artifacts, negating the need for
Docker (i.e. making a throwaway build of dependencies). So in the
meantime, just ignore major version updates of actions/checkout.

Signed-off-by: David Feltell <[email protected]>

Author: feltech

.github/dependabot.yml

@@ -7,3 +7,8 @@ updates:
       interval: "weekly"
     commit-message:
       prefix: "[CI]"
+    ignore:
+      # TODO(DF): Remove once no longer stuck on ASWF CY22 Docker image
+      # for CI (causing nodejs glibc error).
+      - dependency-name: "actions/checkout"
+        update-types: ["version-update:semver-major"]