Merge branch 'jc/ci-update-macos-15'

The macOS CI jobs have been updated to use a mixture of 'macos-15' and
'macos-latest' images, as the 'macos-14' hosted runner image is being
deprecated by GitHub.

* jc/ci-update-macos-15:
  github-ci: update macos jobs from macos-14

.github/workflows/main.yml

@@ -349,16 +349,16 @@ jobs:
         vector:
           - jobname: osx-clang
             cc: clang
-            pool: macos-14
+            pool: macos-15
           - jobname: osx-reftable
             cc: clang
-            pool: macos-14
+            pool: macos-26
           - jobname: osx-gcc
             cc: gcc-13
-            pool: macos-14
+            pool: macos-26
           - jobname: osx-meson
             cc: clang
-            pool: macos-14
+            pool: macos-15
     env:
       CC: ${{matrix.vector.cc}}
       CC_PACKAGE: ${{matrix.vector.cc_package}}