Add checks for Wasm compatibility to pull_request.yml

[MaxDesiatov]

This library currently has no PR testing for Wasm, even though it's a dependency of other libraries that declare Wasm support. To prevent possible future regressions, let's add Wasm build checks to the CI workflows.

rdar://135961596

Checklist

• I've read the Contribution Guidelines
• My contributions are licensed under the Swift license.
• I've followed the coding style of the rest of the project.
• I've added tests covering all new code paths my change adds to the project (if appropriate).
• [N/A] I've added benchmarks covering new functionality (if appropriate).
• I've verified that my change does not break any existing tests or introduce unexplained benchmark regressions.
• [N/A] I've updated the documentation if necessary.

[MaxDesiatov]

@swift-ci test

[MaxDesiatov]

@swift-ci test

[MaxDesiatov]

@swift-ci test

[MaxDesiatov]

@swift-ci test

[lorentey]

Nice! Thank you