Update the `docs` workflow to allow publishing a specific ref (#7278)

Related https://github.com/astral-sh/ruff/issues/7276

Our docs publishing action does not allow targetting a specific commit
when run manually which means we cannot update the documentation to
anything but the latest commit on `main`. This change allows a ref to be
provided.

---------

Co-authored-by: Dhruv Manilawala <dhruvmanila@gmail.com>

.github/workflows/docs.yaml

@@ -2,6 +2,11 @@ name: mkdocs
 
 on:
   workflow_dispatch:
+    inputs:
+      ref:
+        description: "The commit SHA, tag, or branch to publish. Uses the default branch if not specified."
+        default: ""
+        type: string
   release:
     types: [published]
 
@@ -13,6 +18,8 @@ jobs:
       MKDOCS_INSIDERS_SSH_KEY_EXISTS: ${{ secrets.MKDOCS_INSIDERS_SSH_KEY != '' }}
     steps:
       - uses: actions/checkout@v4
+        with:
+          ref: ${{ inputs.ref }}
       - uses: actions/setup-python@v4
       - name: "Add SSH key"
         if: ${{ env.MKDOCS_INSIDERS_SSH_KEY_EXISTS == 'true' }}