Fix support for macOS 14 (#668)

* core-text: define version variable and dbg!() it

Note that this test already has a number of dbg!() calls, presumably
to aid debugging when it fails in the future (for example due to
OS changes).

* core-text: extract helper function in test

* core-text: improve assertion to make failure easier to diagnose

* core-text: allow variations test to pass on 14.x.y

* CI: test on macOS 14

* CI: only test old Rust on one version

.github/workflows/rust.yml

@@ -31,8 +31,11 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [macos-11.0, macos-12, macos-13]
-        toolchain: [stable, 1.56.1]
+        os: [macos-11.0, macos-12, macos-13, macos-14]
+        toolchain: [stable]
+        include:
+          - os: macos-14
+            toolchain: 1.56.1
     steps:
     - uses: actions/checkout@v4
     - name: Install toolchain