github: unset CI for yarn build

Work around https://github.com/facebook/create-react-app/issues/9987

.github/workflows/build-dev.yml

@@ -24,7 +24,7 @@ jobs:
         github-token: ${{ secrets.GITHUB_TOKEN }}
     - name: Build
       if: ${{ success() }}
-      run: yarn build
+      run: CI= yarn build
     - name: Install lftp
       if: ${{ success() }}
       run: sudo apt-get update && sudo apt-get install --yes lftp

.github/workflows/test-pull-request.yml

@@ -30,4 +30,4 @@ jobs:
       uses: coverallsapp/github-action@master
       with:
         github-token: ${{ secrets.GITHUB_TOKEN }}
-    - run: yarn build
+    - run: CI= yarn build