Avoid using macos-latest for jobs we want x86_64 macOS (#1175)

Github actions recently changed the macos-latest runner to use macos-14,
which changes the CI environment to run with arm64 instead of x86_64.
This has several impacts on our test jobs where the intent was to
specifically test native x86_64 macOS. This commit changes the ci
configuration to use macos-13 in places where this was the case, as we
were already explicitly using macos-14 where we wanted arm64 runners.

.github/workflows/main.yml

@@ -59,7 +59,7 @@ jobs:
         rust: [stable]
         python-version: [3.8, 3.9, "3.10", "3.11", "3.12"]
         platform: [
-          { os: "macOS-latest", python-architecture: "x64", rust-target: "x86_64-apple-darwin" },
+          { os: "macOS-13", python-architecture: "x64", rust-target: "x86_64-apple-darwin" },
           { os: "macOS-14", python-architecture: "arm64", rust-target: "aarch64-apple-darwin" },
           { os: "ubuntu-latest", python-architecture: "x64", rust-target: "x86_64-unknown-linux-gnu" },
           { os: "windows-latest", python-architecture: "x64", rust-target: "x86_64-pc-windows-msvc" },

.github/workflows/wheels.yml

@@ -47,7 +47,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, windows-latest, macos-latest, macos-14]
+        os: [ubuntu-latest, windows-latest, macos-13, macos-14]
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v5