CI: Install ansible-core from PyPI

Installing ansible from source leads to reinstallation when installing
ansible-lint, pulling in the latest version, which can fail due to
the ansible-base/ansible-core package being present.

Install from PyPI instead.

Author: markgoddard

.github/workflows/pull_request.yml

@@ -15,18 +15,29 @@ jobs:
       fail-fast: false
       matrix:
         ansible:
-          - stable-2.9
-          - stable-2.10
-          - devel
+          - "2.9"
+          - "2.10"
+          - "2.12"
     steps:
       # Checks-out the repository under $GITHUB_WORKSPACE, so it's accessible to the job
       - uses: actions/checkout@v2
 
+      - uses: actions/setup-python@v2
+
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          pip install git+https://github.com/ansible/ansible.git@${{ matrix.ansible }}
-          pip install 'ansible-lint<5'
+          if [[ "${{ matrix.ansible }}" = "2.9" ]]; then
+              ansible_package=ansible
+          elif [[ "${{ matrix.ansible }}" = "2.10" ]]; then
+              ansible_package=ansible-base
+          else
+              ansible_package=ansible-core
+          fi
+          pip install $ansible_package==${{ matrix.ansible }}.* 'ansible-lint==5.*'
+
+      - name: Install Ansible Galaxy dependencies
+        run: |
           ansible-galaxy collection install pulp.squeezer
 
       - name: Linting code
@@ -39,6 +50,8 @@ jobs:
       # Checks-out the repository under $GITHUB_WORKSPACE, so it's accessible to the job
       - uses: actions/checkout@v2
 
+      - uses: actions/setup-python@v2
+
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip