fix: ensure GITHUB_TOKEN is always set for mise in CI

Fall back to github.token when PROJEN_GITHUB_TOKEN secret is not
configured, so mise's aqua backend can authenticate GitHub API calls
to download tools like trivy without hitting rate limits.

Author: MichaelWalker-git

.github/workflows/build.yml

@@ -75,19 +75,12 @@ const project = new awscdk.AwsCdkTypeScriptApp({
       uses: 'jdx/mise-action@v3.6.2',
       with: {
         cache: true,
-        install: true,
-      },
-      env: {
-        GITHUB_TOKEN: '${{ github.token }}',
-        GITHUB_API_TOKEN: '${{ github.token }}',
       },
     },
   ],
   buildWorkflowOptions: {
     env: {
-      GITHUB_TOKEN: '${{ secrets.PROJEN_GITHUB_TOKEN }}',
-      MISE_GITHUB_TOKEN: '${{ github.token }}',
-      GITHUB_API_TOKEN: '${{ github.token }}',
+      GITHUB_TOKEN: '${{ secrets.PROJEN_GITHUB_TOKEN || github.token }}',
     },
   },
   gitignore: [