Fix REST VOL CI: HSDS now requires Python >= 3.11 (#6662)

The hdf5_vol_rest_fetchcontent job fails at "Install HSDS dependencies"
because HSDS pins numpy==2.4.6, which publishes no distributions for
Python 3.10:

  ERROR: Could not find a version that satisfies the requirement
         numpy==2.4.6 (from versions: ... 2.2.5, 2.2.6)

numpy 2.4.6 declares requires_python >= 3.11, and HSDS's pyproject.toml
now says requires-python = ">=3.11". Move the matrix to Python 3.12,
which is what HSDS uses for its own unix-socket test job - the same
configuration this job exercises.

Also drop the "Fix requests version" step that force-downgraded to
requests==2.31.0. HSDS now pins requests-unixsocket==0.4.1, which fixed
the requests 2.32 breakage that step worked around, so the downgrade only
fights HSDS's own pins. Upstream HSDS has already commented the same step
out of its socket-test job.

Fixes #6657


Claude-Session: https://claude.ai/code/session_011qUw9C11arB1WftiT56EA4

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

.github/workflows/vol_rest.yml

@@ -34,7 +34,10 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ["3.10"]
+        # HSDS requires Python >= 3.11 (its pinned numpy has no 3.10 wheels).
+        # 3.12 matches the Python version HSDS uses for its own unix-socket
+        # test job, which is the configuration exercised here.
+        python-version: ["3.12"]
 
     steps:
       - name: Install dependencies
@@ -129,11 +132,6 @@ jobs:
       #    path: ${{ runner.workspace }}/hsds-${{ env.HSDS_COMMIT_SHORT }}-install
       #    key: ${{ runner.os }}-${{ runner.arch }}-hsds-${{ env.HSDS_COMMIT }}-${{ inputs.build_mode }}-cache
 
-      # Requests 2.32.0 breaks requests-unixsocket, used by HSDS for socket connections
-      - name: Fix requests version
-        run: |
-          pip install requests==2.31.0
-
       - name: Run HSDS unit tests
         shell: bash
         working-directory: ${{github.workspace}}/hsds