Add Wasm build to pull_request.yml

[MaxDesiatov]

This ensures that Wasm builds are tested on CI.

Checklist

• I've run tests to see all new and existing tests pass
• I've followed the code style of the rest of the project
• I've read the Contribution Guidelines
• [N/A] I've updated the documentation if necessary

If you've made changes to gyb files

• [N/A] I've run .script/generate_boilerplate_files_with_gyb and included updated generated files in a commit of this pull request

Motivation:

The library currently doesn't build for Wasm on CI.

Modifications:

• Added Wasm Swift SDK job to pull_request.yml.
• Renamed static-sdk/"Static SDK` job, which is incorrectly named named with vague wording: Musl Swift SDK is not the only one supporting static linking, Wasm is also statically linked by default.

Result:

Build regressions on Wasm are prevented, jobs are named in a non-ambiguous way.