ci: Switch to macOS 14 on M series chips

macOS 12 was released in October 21, and since then 13 has been out in
October 22, and 14 in September 23. Switch to a more recent Mac
operating system since that's likely what users will be running.

See [1] for GitHub's list of available shared runners. From the macos-12
label to the macos-14 label, the number of CPU cores stays the same (3),
but the CPU architecture switches from x86_64 to arm64. All other
parameters stay the same except for RAM, which changes from 14 GB to
7 GB. Since pkcs11-provider is not a memory intensive project, this
likely has negligible impact on us. The new CPU architecture can be
helpful to identify hardware-specific issues, so is probably a net
positive. The M series chips are also typically much faster than the
older Intel counterparts.

[1]: https://docs.github.com/en/actions/using-github-hosted-runners/about-github-hosted-runners/about-github-hosted-runners#standard-github-hosted-runners-for-public-repositories

.github/workflows/build.yml

@@ -89,7 +89,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [macos-12]
+        os: [macos-14]
         token: [softokn, softhsm]
     steps:
       - name: Install Dependencies