Add enable_wasm_sdk_build: true to pull_request.yml

`swift-algorithms` should be built for Wasm as one of the officially supported platforms on CI to prevent possible future regressions.

Author: MaxDesiatov

.github/workflows/pull_request.yml

@@ -21,6 +21,8 @@ jobs:
   tests:
     name: Test
     uses: swiftlang/github-workflows/.github/workflows/swift_package_test.yml@main
+    with:
+      enable_wasm_sdk_build: true
 
   soundness:
     name: Soundness