ci: Remove Python 3.8 fallback to pip install (#2619)

* Use uv for all installations in CI, as the Python 3.8 fall back to
  'pip install' was needed only for TensorFlow.
   - Amends PR #2609

Author: matthewfeickert

.github/workflows/ci.yml

@@ -47,18 +47,10 @@ jobs:
         python-version: ${{ matrix.python-version }}
 
     - name: Install dependencies
-      if: matrix.python-version != '3.8'
       run: |
         python -m pip install uv
         uv pip install --system --upgrade ".[all,test]"
 
-      # c.f. https://github.com/astral-sh/uv/issues/2062
-    - name: Install dependencies (Python 3.8)
-      if: matrix.python-version == '3.8'
-      run: |
-        python -m pip install --upgrade pip
-        python -m pip install --upgrade ".[all,test]"
-
     - name: List installed Python packages
       run: python -m pip list