update swiftpm to depend on swift testing when building using local deps

Author: bkhouri

Package.swift

@@ -58,17 +58,12 @@ let swiftPMDataModelProduct = (
 let usePackageDependencies = ProcessInfo.processInfo.environment["SWIFTCI_USE_LOCAL_DEPS"] == nil
 
 let swiftTestingTargetDep: [Target.Dependency]
-let swiftTestingPackageDeps: [Package.Dependency]
 if !usePackageDependencies {
     swiftTestingTargetDep = [
         .product(name: "Testing", package: "swift-testing"),
     ]
-    swiftTestingPackageDeps = [
-        .package(path: "../swift-testing"),
-    ]
 } else {
     swiftTestingTargetDep = []
-    swiftTestingPackageDeps = []
 }
 
 /** The `libSwiftPM` set of interfaces to programmatically work with Swift
@@ -1030,7 +1025,6 @@ if ProcessInfo.processInfo.environment["SWIFTPM_LLBUILD_FWK"] == nil {
     ]
 }
 
-package.dependencies += swiftTestingPackageDeps
 if usePackageDependencies {
     package.dependencies += [
         .package(url: "https://github.com/swiftlang/swift-tools-support-core.git", branch: relatedDependenciesBranch),
@@ -1056,6 +1050,7 @@ if usePackageDependencies {
         .package(path: "../swift-system"),
         .package(path: "../swift-collections"),
         .package(path: "../swift-certificates"),
+        .package(path: "../swift-testing"),
         .package(path: "../swift-toolchain-sqlite"),
     ]
 }