Update platform support tiers for macOS

CI is switching from x86 runners to aarch64 runners in crystal-lang/crystal#14833

This means, we no longer have automated tests for x86_64-darwin, so it goes into Tier 2. And aarch64-darwin moves up to Tier 1.

docs/syntax_and_semantics/platform_support.md

@@ -19,7 +19,7 @@ and drop into *Tier 2*.
 
 | Target | Description | Supported versions | Comment |
 | ------ | ----------- | ------------------ | ------- |
-| `x86_64-darwin` | x64 macOS<br> (Intel) | 11+<br> *(testing only on 11; expected to work on 10.7+)* | :material-checkbox-marked-circle: tests<br> :material-checkbox-marked-circle: builds
+| `aarch64-darwin` | Aarch64 macOS<br> (Apple Silicon) | 11+ *(testing only on 14)* | :material-selection-circle: tests<br> :material-checkbox-marked-circle: builds
 | `x86_64-linux-gnu` | x64 Linux | kernel 4.14+, GNU libc 2.26+<br> *(expected to work on kernel 2.6.18+)* | :material-checkbox-marked-circle: tests<br> :material-checkbox-marked-circle: builds
 | `x86_64-linux-musl` | x64 Linux | kernel 4.14+, MUSL libc 1.2+<br> *(expected to work on kernel 2.6.18+)* | :material-checkbox-marked-circle: tests<br> :material-checkbox-marked-circle: builds
 
@@ -34,14 +34,14 @@ Details are described in the *Comment* column.
 
 | Target | Description | Supported versions | Comment |
 | ------ | ----------- | ------------------ | ------- |
-| `aarch64-darwin` | Aarch64 macOS<br> (Apple Silicon) | 11+ | :material-selection-ellipse: tests<br> :material-checkbox-marked-circle: builds
 | `aarch64-linux-gnu` | Aarch64 Linux | GNU libc 2.26+ | :material-checkbox-marked-circle: tests<br> :material-selection-ellipse: builds
 | `aarch64-linux-musl` | Aarch64 Linux | MUSL libc 1.2+ | :material-checkbox-marked-circle: tests<br> :material-selection-ellipse: builds
 | `arm-linux-gnueabihf` | Aarch32 Linux<br> (hardfloat) | GNU libc 2.26+ | :material-selection-ellipse: tests<br> :material-selection-ellipse: builds
 | `i386-linux-gnu` | x86 Linux | kernel 4.14+, GNU libc 2.26+<br> *(expected to work on kernel 2.6.18+)* | :material-selection-ellipse: tests<br> :material-selection-ellipse: builds
 | `i386-linux-musl` | x86 Linux | kernel 4.14+, MUSL libc 1.2+<br> *(expected to work on kernel 2.6.18+)* | :material-selection-ellipse: tests<br> :material-selection-ellipse: builds
 | `x86_64-openbsd` | x64 OpenBSD | 6+ | :material-selection-ellipse: tests<br> :material-selection-ellipse: builds
 | `x86_64-freebsd` | x64 FreeBSD | 12+ | :material-selection-ellipse: tests<br> :material-selection-ellipse: builds
+| `x86_64-darwin` | x64 macOS<br> (Intel) | 10.7+ | :material-checkbox-marked-ellipse: tests<br> :material-checkbox-marked-circle: builds
 
 ***