[stdlib][test] Update string printing availability checks

The change in behaviour that these checks covered is not currently in 6.0,
only in main. Update the availability check to use stdlib 6.1.

Author: benlangmuir

test/stdlib/BridgedObjectDebuggerSupport.swift

@@ -78,8 +78,10 @@ StringForPrintObjectTests.test("NSStringUTF8") {
   expectEqual("🏂☃❅❆❄︎⛄️❄️", String(reflecting: nsUTF16))
   expectEqual("\"🏂☃❅❆❄︎⛄️❄️\"", String(reflecting: newNSUTF16))
 
-  if #available(SwiftStdlib 6.0, *) {
+  if #available(SwiftStdlib 6.1, *) {
     expectEqual("🏂☃❅❆❄︎⛄️❄️\n", printed)
+  } else {
+    expectEqual("\"🏂☃❅❆❄︎⛄️❄️\"\n", printed)
   }
 
   expectEqual(printed, debug)

test/stdlib/DebuggerSupport.swift

@@ -101,11 +101,16 @@ StringForPrintObjectTests.test("DontBridgeThisStruct") {
 }
 #endif
 
-if #available(SwiftStdlib 6.0, *) {
+if #available(SwiftStdlib 6.1, *) {
   StringForPrintObjectTests.test("String") {
     let printed = _stringForPrintObject("hello\nworld")
     expectEqual(printed, "hello\nworld\n")
   }
+} else {
+  StringForPrintObjectTests.test("String") {
+    let printed = _stringForPrintObject("hello\nworld")
+    expectEqual(printed, "\"hello\\nworld\"\n")
+  }
 }
 
 class RefCountedObj {