ubuntu-18.04を除外 (#18)

Author: Hiroshiba

.github/workflows/general.yml

@@ -114,8 +114,8 @@ jobs:
           - os: macos-10.15
           - os: macos-11
           - os: macos-12
-          - os: ubuntu-18.04
           - os: ubuntu-20.04
+          - os: ubuntu-22.04
     runs-on: ${{ matrix.os }}
     steps:
       - name: Install LLVM and Clang # required for bindgen to work, see https://github.com/rust-lang/rust-bindgen/issues/1797