[Github] Use hashed dependencies in docs job (#120319)

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