(maint) Hardcodes macOS runner as 11 in Actions

Author: mhashizume

.github/actions/presuite.rb

@@ -32,7 +32,7 @@ def initialize_beaker
 def beaker_platform
   {
     'ubuntu-20.04' => 'ubuntu2004-64a',
-    'macos-latest' => 'osx11-64a',
+    'macos-11' => 'osx11-64a',
     'windows-2016' => 'windows2016-64a',
     'windows-2019' => 'windows2019-64a'
   }[HOST_PLATFORM]

.github/workflows/acceptance_tests.yml

@@ -14,7 +14,7 @@ jobs:
     name: Platform
     strategy:
       matrix:
-        os: [ windows-2019, ubuntu-20.04, macos-latest ]
+        os: [ windows-2019, ubuntu-20.04, macos-11 ]
     runs-on: ${{ matrix.os }}
     env:
       BEAKER_debug: true