Tests: remove @testable import SPMBuildCore

Use the newly extended APIs for testing and use a non-testable import of
the package, avoiding a recompilation.

Author: compnerd

Tests/BuildTests/PluginInvocationTests.swift

@@ -21,7 +21,7 @@ import PackageLoading
 @_spi(SwiftPMInternal)
 import PackageModel
 
-@testable import SPMBuildCore
+import SPMBuildCore
 import _InternalBuildTestSupport
 import _InternalTestSupport
 import Workspace

Tests/BuildTests/PluginsBuildPlanTests.swift

@@ -12,7 +12,7 @@
 
 import Basics
 import _InternalTestSupport
-@testable import SPMBuildCore
+import SPMBuildCore
 import XCTest
 import PackageModel
 

Tests/FunctionalTests/PluginTests.swift

@@ -17,7 +17,7 @@ import _Concurrency
 import PackageGraph
 import PackageLoading
 import PackageModel
-@testable import SPMBuildCore
+import SPMBuildCore
 import _InternalTestSupport
 import Workspace
 import Testing

Tests/PackageModelTests/SwiftSDKTests.swift

@@ -15,7 +15,7 @@ import Basics
 @_spi(SwiftPMInternal)
 import PackageModel
 
-@testable import SPMBuildCore
+import SPMBuildCore
 import XCTest
 
 private let bundleRootPath = try! AbsolutePath(validating: "/tmp/cross-toolchain")

Tests/SPMBuildCoreTests/BuildParametersTests.swift

@@ -10,7 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-@testable import SPMBuildCore
+import SPMBuildCore
 import Basics
 import struct PackageModel.BuildEnvironment
 import _InternalTestSupport