[PATCH] github-ci: update macos jobs to macos-15

[Junio C Hamano <gitster@pobox.com>]

GitHub from <no-reply@github.com> address keeps sending

  Subject: [Action Required] macOS 14 hosted runner image is closing down

and suggests to update to either macos-latest (macos-26) or
macos-15.  As we do not have strong reason to pick one over the
other, this patch picks more conservative choice with hopefully
smaller impact.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 * Not tested at all and I do not do macos myself.

 .github/workflows/main.yml | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git i/.github/workflows/main.yml w/.github/workflows/main.yml
index b229739be8..d69f6f2b10 100644
--- i/.github/workflows/main.yml
+++ w/.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-15
           - jobname: osx-gcc
             cc: gcc-13
-            pool: macos-14
+            pool: macos-15
           - jobname: osx-meson
             cc: clang
-            pool: macos-14
+            pool: macos-15
     env:
       CC: ${{matrix.vector.cc}}
       CC_PACKAGE: ${{matrix.vector.cc_package}}