ci: switch macos runs from macos-12 to macos-13

macOS 13 was released in Oct 2022 and the GitHub Actions image debuted
Apr 2023. Let's switch to this new platform.

It seems to work fine based on two runs testing the nice fix in the
previous patch.

https://github.com/vincentkfu/fio/actions/runs/6352923622/job/17256648185
https://github.com/vincentkfu/fio/actions/runs/6353159388/job/17257286332

Signed-off-by: Vincent Fu <vincent.fu@samsung.com>

.github/workflows/ci.yml

@@ -27,7 +27,7 @@ jobs:
  os: ubuntu-22.04
  cc: clang
  - build: macos
- os: macos-12
+ os: macos-13
  - build: linux-i686-gcc
  os: ubuntu-22.04
  arch: i686