Fix CI: CI does not use the promised Rust version

[phip1611]

By experiments, I found out that the current Github CI does not use the specified Rust version. I could verify this by using "1.30.0", an old version that definitely does not work.

Minimal Reproducible Example

jobs:
  build:
    runs-on: ubuntu-latest
    strategy:
      matrix:
        rust:
          - 1.30.0 # MSVR
    steps:
      - uses: actions/checkout@v2
      - run: cargo --version
      - uses: actions-rs/cargo@v1
        with:
          command: version

Both commands return 1.60.0 which is the current latest stable version.