build: fix syntax error in GH-hosted tests workflow (openedx#31105)

We were seeing this error whenever unit tests
were run from a fork (only forks use the GH-hosted
workflow, which is why this was able to merge
into master):

  You have an error in your yaml syntax on line 65

The comment hash (#) needs to be aligned
with the rest of the text block.

.github/workflows/unit-tests-gh-hosted.yml

@@ -67,7 +67,7 @@ jobs:
         run: |
             pip install -r requirements/pip.txt
             pip install -r requirements/edx/development.txt --src ${{ runner.temp }}
-#            edx-platform installs some Python projects from within the edx-platform repo itself.
+            # edx-platform installs some Python projects from within the edx-platform repo itself.
             pip install -e .
             pip install "django~=${{ matrix.django-version }}.0"