ScriptValidation: Make break/next a warning until Zeek 6.1

The ja3 package uses next instead of return and triggers the new
errors with Zeek 5.2. That seems somewhat bad.

In case we want to do a 5.2.1 that makes this a warning, this
would be change to do so.

testing/btest/language/next-break-context-errors.zeek

@@ -1,6 +1,6 @@
 # @TEST-DOC: Check break and next usage within for, while, switch and hooks.
 
-# @TEST-EXEC-FAIL: zeek -b %INPUT
+# @TEST-EXEC: zeek -b %INPUT
 # @TEST-EXEC: TEST_DIFF_CANONIFIER=$SCRIPTS/diff-remove-abspath btest-diff .stderr
 function f()
 	{