use python3 for CI builds

Author: svartalf

.github/workflows/build-cache.yml

@@ -18,12 +18,14 @@ jobs:
           - cargo-audit
           - cargo-udeps
           - cargo-nono
+          - cross
+          - sccache
     steps:
       - uses: actions/checkout@v2
       - name: Build and upload binary crate
         run: |
-          python -m pip install -r ci/requirements.txt
-          python ci/build.py
+          python3 -m pip install -r ci/requirements.txt
+          python3 ci/build.py
         env:
           CRATE: ${{ matrix.crate }}
           RUNNER: ${{ matrix.os }}