Appending valid encoding character can change coderange from invalid to valid.
Example: "\x95".force_encoding('sjis')<<0x5C will be a valid string "\x{955C}"
Related issues
Bug #20190: `invalid_encoding_string << number` should be valid encoding in some case, but does not
merge revision(s) ade56737e2273847426214035c0ff2340b43799a: [Backport #20190] (#10300)
Fix coderange of invalid_encoding_string.<<(ord)