test: Add a helper to check the next line against a regex

Add a new ut_assert_nextline_regex() macro and ut_check_console_line_regex()
helper to check console output against a regex pattern. This is useful when
the exact output varies (e.g., file paths or line numbers in error messages).

Co-developed-by: Claude <noreply@anthropic.com>
Signed-off-by: Simon Glass <simon.glass@canonical.com>

doc/develop/tests_writing.rst

@@ -451,6 +451,9 @@ ut_assert_nextlinen(fmt, args...)
     Assert that the next console output line matches up to the format
     string length
 
+ut_assert_nextline_regex(pattern)
+    Assert that the next console output line matches a regex pattern
+
 ut_assert_nextline_empty()
     Assert that the next console output line is empty