Revert "mach: switch to uv for managing python venv (#34504)" (#34548)

This reverts commit 4103421ba5.

Signed-off-by: Mukilan Thiyagarajan <mukilan@igalia.com>

.github/workflows/mac.yml

@@ -77,14 +77,18 @@ jobs:
         if: github.event_name == 'pull_request_target'
         with:
           ref: ${{ github.event.pull_request.head.sha }}
-      - name: Setup Python
-        uses: ./.github/actions/setup-python
+      # Python 3.13 breaks wptrunner, so pin the version until
+      # web-platform-tests/wpt#48585 is fixed.
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
       - name: Run sccache-cache
         uses: mozilla-actions/sccache-action@v0.0.6
       - name: Install crown
         run: cargo install --path support/crown
       - name: Bootstrap
         run: |
+          python3 -m pip install --upgrade pip
           python3 ./mach bootstrap --skip-lints
           brew install gnu-tar
       - name: Build (${{ inputs.profile }})