Changing Flutter Candidate to 3.22.0-42.0.pre (#7798)

Automated Flutter candidate version bump.

flutter-candidate.txt

diff --git a/flutter-candidate.txt b/flutter-candidate.txt
index 2468a24..94d3552 100644
--- a/flutter-candidate.txt
+++ b/flutter-candidate.txt
@@ -1 +1 @@
-3.22.0-39.0.pre
+3.22.0-42.0.pre