[TEST] fix branch name

Author: mmcky

.github/workflows/execution.yml

@@ -24,7 +24,7 @@ jobs:
         run: |
           conda install anaconda
           pip install jupyter-book sphinx-multitoc-numbering quantecon-book-theme sphinxext-rediraffe sphinx_tojupyter
-          pip install git+https://github.com/executablebooks/MyST-NB@ga-windows-testing
+          pip install git+https://github.com/executablebooks/MyST-NB@code-load-utf8-standard
       - name: Build Lectures (+ Execution Checks)
         shell: bash -l {0}
         run: jb build lectures --path-output=./ -W --keep-going