update wit-abi-up-to-date to parse @since gates

Author: yoshuawuyts

.github/workflows/main.yml

@@ -11,4 +11,4 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v4
-    - uses: WebAssembly/wit-abi-up-to-date@v17
+    - uses: WebAssembly/wit-abi-up-to-date@v21