CI: use ccache for default build jobs

These are built repeatedly, often with no changes in source code

.github/workflows/macos_build.yml

@@ -25,6 +25,10 @@ jobs:
       # ... but in the repo, we want to test pyenv builds on macOS
       - run: |
           brew install openssl readline sqlite3 xz zlib
+      - name: Ccache for gh actions
+        uses: hendrikmuhs/ccache-action@v1.2.17
+        with:
+          key: ${{ github.job }}-${{ matrix.python-version}}
         # https://github.com/pyenv/pyenv#installation
       - run: pwd
       - env:

.github/workflows/ubuntu_build.yml

@@ -27,6 +27,10 @@ jobs:
           sudo apt-get update -q; sudo apt install -yq make build-essential libssl-dev zlib1g-dev \
           libbz2-dev libreadline-dev libsqlite3-dev curl \
           libncursesw5-dev xz-utils tk-dev libxml2-dev libxmlsec1-dev libffi-dev liblzma-dev
+      - name: Ccache for gh actions
+        uses: hendrikmuhs/ccache-action@v1.2.17
+        with:
+          key: ${{ github.job }}-${{ matrix.python-version}}
         # https://github.com/pyenv/pyenv#installation
       - run: pwd
       - env: