Update bazel to 6.3.2

Demote the errorprone pattern PreferredInterfaceType aka
MutableMethodReturnType to ensure the build still succeeds.

Change-Id: I6a6e44362e6ff943a26553890a2c84dbfe65128b

.bazelversion

diff --git a/.bazelversion b/.bazelversion
index 0062ac9..91e4a9f 100644
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1 @@
-5.0.0
+6.3.2