Post branch adjustments for 5.9 (#6324)

Author: neonichu

Package.swift

@@ -696,7 +696,7 @@ let package = Package(
 // this right now.
 
 /// When not using local dependencies, the branch to use for llbuild and TSC repositories.
-let relatedDependenciesBranch = "main"
+let relatedDependenciesBranch = "release/5.9"
 
 if ProcessInfo.processInfo.environment["SWIFTPM_LLBUILD_FWK"] == nil {
     if ProcessInfo.processInfo.environment["SWIFTCI_USE_LOCAL_DEPS"] == nil {

Sources/Basics/SwiftVersion.swift

@@ -55,7 +55,7 @@ extension SwiftVersion {
     /// The current version of the package manager.
     public static let current = SwiftVersion(
         version: (5, 9, 0),
-        isDevelopment: true,
+        isDevelopment: false,
         buildIdentifier: getBuildIdentifier()
     )
 }