Replace @testable with @_spi(Testing)

Author: DougGregor

Sources/SourceKitLSP/Swift/CodeActions/ConvertJSONToCodableStruct.swift

@@ -55,8 +55,10 @@ import SwiftSyntax
 ///   }
 /// }
 /// ```
-struct ConvertJSONToCodableStruct: EditRefactoringProvider {
-  static func textRefactor(
+@_spi(Testing)
+public struct ConvertJSONToCodableStruct: EditRefactoringProvider {
+  @_spi(Testing)
+  public static func textRefactor(
     syntax: Syntax,
     in context: Void
   ) -> [SourceEdit] {

Tests/SourceKitLSPTests/SyntaxRefactorTests.swift

@@ -15,7 +15,7 @@ import SwiftRefactor
 import SwiftSyntax
 import XCTest
 
-@testable import SourceKitLSP
+@_spi(Testing) import SourceKitLSP
 
 final class SyntaxRefactorTests: XCTestCase {
   func testConvertJSONToCodableStructClosure() throws {