Ensure Homebrew is loaded; drop support for Python 3.7 due to lack of ARM64 macOS build by Homebrew

.github/workflows/python.yml

@@ -13,7 +13,7 @@ jobs:
       matrix:
         feature: [core, js]
         os: [macos-11.0, ubuntu-18.04, windows-2019, self-hosted-linux-arm64, self-hosted-macos-arm64]
-        python: [3.7, 3.8, 3.9, '3.10']
+        python: [3.8, 3.9, '3.10']
     steps:
       - uses: actions/checkout@v1
 
@@ -34,6 +34,8 @@ jobs:
       - name: Set up Python (macOS ARM64)
         if: runner.name == 'macos-arm64'
         run: |
+          eval "$(/opt/homebrew/bin/brew shellenv)"
+          export HOMEBREW_NO_INSTALL_CLEANUP=1
           brew unlink python
           brew link python@${{ matrix.python }}
 
@@ -97,6 +99,8 @@ jobs:
             eval "$(pyenv init --path)"
           fi
           if [[ "${{ runner.name }}" == macos-arm64 ]]; then
+            eval "$(/opt/homebrew/bin/brew shellenv)"
+            export HOMEBREW_NO_INSTALL_CLEANUP=1
             pathToPython="$(which python3)"
           else
             pathToPython="$(which python)"