Removve macOS 11 GitHub Actions runners

- GitHub removed these runners, so the build will no longer run on them

Author: bluk

.github/workflows/ci.yml

@@ -23,9 +23,6 @@ jobs:
         exclude:
           - os: macos-latest
             rust: 1.36.0
-        include:
-          - os: macos-11
-            rust: 1.36.0
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout sources
@@ -58,9 +55,6 @@ jobs:
         exclude:
           - os: macos-latest
             rust: 1.56.0
-        include:
-          - os: macos-11
-            rust: 1.56.0
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout sources