Remove macos-13 from CI. NFC (#2661)

GitHub are removing support:
actions/runner-images#13046

Author: sbc100

.github/workflows/build.yml

@@ -32,7 +32,7 @@ jobs:
       matrix:
         # Temporarily replaced macos-latest with macos-14.
         # See https://github.com/WebAssembly/wabt/issues/2654
-        os: [ubuntu-latest, macos-13, macos-14, windows-latest]
+        os: [ubuntu-latest, macos-14, windows-latest]
     steps:
     - uses: actions/setup-python@v5
       with: