Use macos-13 runner for x86 neovim build

Author: qvacua

.github/workflows/build-universal-neovim.yml

@@ -12,7 +12,7 @@ jobs:
       matrix:
         runner: [ macos-13, macos-14 ]
         include:
-          - runner: macos-12
+          - runner: macos-13
             arch: x86_64
           - runner: macos-14
             arch: arm64