Scrub invalid UTF-8 bytes from debuggee output in tests

setup_remote_debuggee reads lines from PTY and matches them against
regexps, but Regexp#=== raises ArgumentError when the line contains
invalid UTF-8 byte sequences. This has been causing random CI failures:
https://github.com/ruby/ruby/actions/runs/23754369209/job/69204936437

Use String#scrub to replace invalid bytes before matching.

Author: k0kubun

test/support/test_case.rb

@@ -173,6 +173,7 @@ def setup_remote_debuggee(cmd)
 
       Timeout.timeout(TIMEOUT_SEC) do
         line = remote_info.r.gets
+        line = line.scrub if line
         remote_info.debuggee_backlog << line
 
         # wait for two lines (order is unstable)