Clarify reason for configuring a CI git user

Author: unstubbable

.github/workflows/build_reusable.yml

@@ -133,7 +133,8 @@ jobs:
       # clean up any previous artifacts to avoid hitting disk space limits
       - run: git clean -xdf && rm -rf /tmp/next-repo-*; rm -rf /tmp/next-install-* /tmp/yarn-* /tmp/ncc-cache target
 
-      - name: Set CI git user for CNA
+      # Configure a git user so that Create Next App can initialize git repos during integration tests.
+      - name: Set CI git user
         run: |
           git config --global user.name "vercel-ci-bot"
           git config --global user.email "[email protected]"