ci: bump validate-plugins action pin to self-healing CLI install

Bumps the pinned validate-plugins action SHA (f846a0bc -> 5d75f99) to pick up
two fixes already merged in claude-plugins-community:

1. Self-healing claude CLI install (community#233): the prior pin's install step
   was a bare `npm i -g @anthropic-ai/claude-code@latest && claude --version`,
   which intermittently stalled (a 28-min hang -> "native binary not installed")
   and jammed whichever bump PR caught it (e.g. desktop-commander #2985). The new
   step forces the optional native dep, verifies the binary, re-runs the
   postinstall on a miss, and bounds every network step with a timeout.

2. strict:false skills-only manifest synthesis: the prior pin hard-required a
   plugin.json for external git-subdir sources, false-failing skills-only entries
   that the marketplace server synthesizes a manifest for. This is what blocks
   #2997 (learn-with-coursera) and #2312 (netsuite-suitecloud) today; the bumped
   action synthesizes a minimal manifest for them instead.

No other change. The action stays on claude-cli-version: latest.

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

.github/workflows/validate-plugins.yml

@@ -32,7 +32,7 @@ jobs:
         with:
           fetch-depth: 0
 
-      - uses: anthropics/claude-plugins-community/.github/actions/validate-plugins@f846a0bcb0e721b1f93d60e8b73e91dafc4a1e87
+      - uses: anthropics/claude-plugins-community/.github/actions/validate-plugins@5d75f9912fedf8609e56fa7c7f9d717581c98a3d
         with:
           marketplace-path: .claude-plugin/marketplace.json
           # Official curated marketplace: SHA-pin (I5) is a HARD error.