chore(bump-plugin-shas): re-pin to community 426e469f (subdir-existence guard #267)

Picks up anthropics/claude-plugins-community#267 — guards subdir existence
before manifest synthesis, so a strict:false external whose source.path subdir
vanished at the new SHA is a clean "subdir not found" skip instead of a phantom
synthesized manifest + false bump. Clean one-commit pull-forward from a27629fc.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/workflows/bump-plugin-shas.yml

@@ -57,7 +57,7 @@ jobs:
 
       # createCommitOnBranch-based bump so commits are signed by GitHub and
       # satisfy the org-level required_signatures ruleset on main.
-      - uses: anthropics/claude-plugins-community/.github/actions/bump-plugin-shas@a27629fc8c11488cc3e25ec527bb28196c5db04f
+      - uses: anthropics/claude-plugins-community/.github/actions/bump-plugin-shas@426e469f322952061102b286b378c0c9733a0934
         id: bump
         with:
           marketplace-path: .claude-plugin/marketplace.json