update GitHub Actions runners (#342)

Author: davepacheco

.github/workflows/rust.yml

@@ -43,7 +43,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ ubuntu-20.04, windows-2022, macos-12 ]
+        os: [ ubuntu-24.04, windows-2022, macos-14 ]
     steps:
     # actions/checkout@v2
     - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683