[build-presets] Test SourceKit-LSP in the swift-syntax macOS job

SourceKit-LSP depends on swift-syntax sufficiently much that changed runtime behavior of swift-syntax can make sourcekit-lsp fail, as it happened in swiftlang/sourcekit-lsp#1110.

Only testing sourcekit-lsp on macOS, not Linux for now. Testing on one platform should be sufficient.

Author: ahoppen

utils/build-presets.ini

@@ -1878,6 +1878,7 @@ swiftsyntax-lint
 swiftformat
 skstresstester
 sourcekit-lsp
+test-sourcekit-lsp
 install-swiftformat
 skip-test-swift=false