Updates to Windows CI

- Pin version of pip
  -  See actions/runner-images#5027
- Target Windows 2019

Signed-off-by: Jacob Perron <jacob@openrobotics.org>

.github/workflows/CI.yml

@@ -6,7 +6,7 @@ jobs:
       fail-fast: false
       matrix:
           rosdistro: [foxy]
-          os: [ubuntu-20.04, windows-latest]
+          os: [ubuntu-20.04, windows-2019]
     runs-on: ${{ matrix.os }}
     steps:
     - if: runner.os == 'Windows'
@@ -18,6 +18,9 @@ jobs:
     - if: runner.os == 'Linux'
       # azure ubuntu repo can be flaky so add an alternate source
       run: sed -e 's/azure.archive.ubuntu.com/us.archive.ubuntu.com/g' -e t -e d /etc/apt/sources.list | sudo tee /etc/apt/sources.list.d/nonazure.list
+    - if: runner.os == 'Windows'
+      name: Pin pip
+      run: python -m pip install -U pip==21.3.1
     - name: Acquire ROS dependencies
       uses: ros-tooling/setup-ros@v0.2
       with: