[Github] Use hashed dependencies in docs job

This patch forces the docs test build job to use the hashed dpendencies file
rather than the normal requirements.txt. This ensures that we get the exact
transitive closure specified rather than whatever the dependency solver feels
like it should use in the CI job.

.github/workflows/docs.yml

@@ -106,9 +106,9 @@ jobs:
         with:
           python-version: '3.11'
           cache: 'pip'
-          cache-dependency-path: 'llvm/docs/requirements.txt'
+          cache-dependency-path: 'llvm/docs/requirements-hashed.txt'
       - name: Install python dependencies
-        run: pip install -r llvm/docs/requirements.txt
+        run: pip install -r llvm/docs/requirements-hashed.txt
       - name: Install system dependencies
         run: |
           sudo apt-get update