update macos version for runner

[fedordikarev]

Closes: https://github.com/neondatabase/neon/issues/9816

According to the workflow file we install icu4c with brew install, so that should work. Lets verify that, and if it works, I will check why it fails on my PR and what needed to be fixed there.

Anyway, lets run on macos-15

[github-actions[bot]]

5517 tests run: 5291 passed, 0 failed, 226 skipped (full report)

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Flaky tests (1)

#### Postgres 14 - `test_pull_timeline[True]`: [release-x86-64](https://neon-github-public-dev.s3.amazonaws.com/reports/pr-9817/11931806973/index.html#suites/82004ab4e3720b47bf78f312dabe7c55/69461ebd36588feb/retries)

Code coverage* (full report)

• functions: 31.4% (7939 of 25297 functions)
• lines: 49.3% (63000 of 127719 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
e5024a5c05016c30dec7897aca22d1040a340f63 at 2024-11-20T11:49:16.823Z :recycle:}