fix: resolve pnpm version conflicts in FlakeGuard workflows

- Update pnpm version from 'latest' to '10.0.0' in FlakeGuard workflows
- Align with root package.json packageManager specification: pnpm@10.0.0
- Fixes workflow failures due to version mismatch between:
  - .github/workflows/*.yml (was using 'latest')
  - package.json packageManager field (specifies 'pnpm@10.0.0')

Updated workflows:
- .github/workflows/flakeguard.yml
- .github/workflows/pr-notifications.yml
- .github/workflows/quarantine-pr.yml

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: thc1006

.github/workflows/flakeguard.yml

@@ -32,7 +32,7 @@ jobs:
       - name: Setup pnpm
         uses: pnpm/action-setup@v4
         with:
-          version: latest
+          version: 10.0.0
 
       - name: Register FlakeGuard problem matcher
         run: echo "::add-matcher::.github/matchers/flakeguard.json"

.github/workflows/pr-notifications.yml

@@ -31,7 +31,7 @@ jobs:
       - name: Setup pnpm
         uses: pnpm/action-setup@v4
         with:
-          version: latest
+          version: 10.0.0
 
       - name: Install dependencies
         run: pnpm install --frozen-lockfile
@@ -257,7 +257,7 @@ jobs:
       - name: Setup pnpm
         uses: pnpm/action-setup@v4
         with:
-          version: latest
+          version: 10.0.0
 
       - name: Install dependencies
         run: pnpm install --frozen-lockfile

.github/workflows/quarantine-pr.yml

@@ -28,7 +28,7 @@ jobs:
       - name: Setup pnpm
         uses: pnpm/action-setup@v4
         with:
-          version: latest
+          version: 10.0.0
 
       - name: Install dependencies
         run: pnpm install --frozen-lockfile
@@ -148,7 +148,7 @@ jobs:
       - name: Setup pnpm
         uses: pnpm/action-setup@v4
         with:
-          version: latest
+          version: 10.0.0
 
       - name: Install dependencies
         run: pnpm install --frozen-lockfile
@@ -216,7 +216,7 @@ jobs:
       - name: Setup pnpm
         uses: pnpm/action-setup@v4
         with:
-          version: latest
+          version: 10.0.0
 
       - name: Install dependencies
         run: pnpm install --frozen-lockfile