Update GitHub Actions workflows to install pnpm version 10.26.2 for consistency across build and validation processes.

.github/workflows/build.yml

@@ -17,6 +17,8 @@ jobs:
 
       - uses: pnpm/action-setup@v4
         name: Install pnpm
+        with:
+          version: 10.26.2
 
       - name: Install system dependencies for canvas and rsvg-convert
         run: |

.github/workflows/validate-pr.yml

@@ -38,6 +38,8 @@ jobs:
 
       - uses: pnpm/action-setup@v4
         name: Install pnpm
+        with:
+          version: 10.26.2
 
       - name: Get pnpm store directory
         shell: bash