Replace macos-12 runner by macos-15

The macos-12 runner is no longer available.

Change-Id: Ib559bf949f423d2bcc350686dbc829b72fe9a9bb

.github/workflows/macos.yml

diff --git a/.github/workflows/macos.yml b/.github/workflows/macos.yml
index 344eef3..ee078e5 100644
--- a/.github/workflows/macos.yml
+++ b/.github/workflows/macos.yml
@@ -16,9 +16,9 @@
       fail-fast: true
       matrix:
         os:
-          - macos-12
           - macos-13
           - macos-14
+          - macos-15
         build_type:
           - Release
         lib: