[CI] macOS 11 is no longer available on GHA (#1928)

Author: JasonGross

.github/workflows/coq-macos.yml

@@ -17,9 +17,9 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        # macOS 11, 12, 13 are x86_64; macOS 14 is arm64
+        # macOS 12, 13 are x86_64; macOS 14 is arm64
         include:
-        - os: { name: 'macOS 11', arch: 'x86_64', runs-on: 'macos-11' } # move to macOS-12 when 11 is removed
+        - os: { name: 'macOS 12', arch: 'x86_64', runs-on: 'macos-12' }
           ocaml-compiler: '4.11.1'
         - os: { name: 'macOS 14', arch: 'arm64' , runs-on: 'macos-14' }
           ocaml-compiler: '4.14.2'
@@ -146,10 +146,8 @@ jobs:
       fail-fast: false
       matrix:
         arch: ['', '-x86_64', '-arm64']
-        os: ['macos-11', 'macos-12', 'macos-13', 'macos-14', 'macos-latest']
+        os: ['macos-12', 'macos-13', 'macos-14', 'macos-latest']
         exclude:
-          - os: 'macos-11'
-            arch: '-arm64'
           - os: 'macos-12'
             arch: '-arm64'
           - os: 'macos-13'