Drop retired macos-14 runner from macOS workflow

GitHub is retiring the macos-14 runner image in November-December 2026
(https://github.com/actions/runner-images/issues/13518). Remove macos-14
from the macOS CI matrix and run host and iOS builds on macos-15.

Change-Id: I2c5e4b92f8d105e3a940d8326f1b92d55c37a122

.github/workflows/macos.yml

diff --git a/.github/workflows/macos.yml b/.github/workflows/macos.yml
index bba4754..be7bb5a 100644
--- a/.github/workflows/macos.yml
+++ b/.github/workflows/macos.yml
@@ -16,7 +16,6 @@
       fail-fast: true
       matrix:
         os:
-          - macos-14
           - macos-15
         build_type:
           - Release