chore(ci): migrate from macos-13 to macos-15-intel runner

GitHub announced the deprecation of the `macos-13` runner image[^1],
which will be completely removed by December 4th, 2025.

This commit migrates all workflows to use `macos-15-intel` runners
following the announcement's recommendation.

This also uses `ubuntu-latest` alias instead of explicit `ubuntu-24.04`.

[^1]: https://github.blog/changelog/2025-09-19-github-actions-macos-13-runner-image-is-closing-down/

Signed-off-by: Aofei Sheng <aofei@aofeisheng.com>

.github/workflows/go.yml

@@ -5,7 +5,7 @@ name: Go
 
 on:
   push:
-    branches: 
+    branches:
       - "**"
       - "!dependabot/**"
   pull_request:
@@ -23,7 +23,7 @@ jobs:
       matrix:
         os:
           - macos-latest
-          - ubuntu-24.04
+          - ubuntu-latest
         llvm: [19]
     runs-on: ${{matrix.os}}
     steps: