Use matrix.os for macos workflow "runs-on"

Previously was using macos-latest regardless of the value of
matrix.os. Should now use macOS 12, 13 and Latest.

.github/workflows/macos.yaml

@@ -28,9 +28,8 @@ concurrency:
 
 jobs:
  macos:
- name: test macos with libevent
- runs-on: macos-latest
-
+ name: macOS with Libevent
+
  strategy:
  fail-fast: false
  matrix:
@@ -40,6 +39,8 @@ jobs:
  tls: [ 'true', 'false' ]
  def_debug: [ 'true', 'false' ]
 
+ runs-on: ${{ matrix.os }}
+
  steps:
  - name: Install dependencies (macOS)
  if: contains(matrix.os, 'macos')