Fix cppcheck filter to match newline before checkers line

Changed regex to \nnofile...\n and replace with \n to properly
remove the checkers report line and its surrounding newlines while
preserving one trailing newline.

Author: pocc

tests/test_hooks.py

@@ -413,7 +413,7 @@ def run_integration_test(cmd_name, files, args, test_dir, target_output, target_
 
         # Newer cppcheck versions include a checkers report info line
         if cmd_name == "cppcheck":
-            output_actual = re.sub(rb"nofile:0:0: information: Active checkers.*\n", b"", output_actual)
+            output_actual = re.sub(rb"\nnofile:0:0: information: Active checkers.*\n", b"\n", output_actual)
 
         utils.assert_equal(target_output, output_actual)
         assert target_retcode == actual_returncode
@@ -454,7 +454,7 @@ def run_shell_cmd(cmd_name, files, args, _, target_output, target_retcode):
             actual = re.sub(rb"[\d,]+ warnings and ", b"", actual)
         # Newer cppcheck versions include a checkers report info line
         if cmd_name == "cppcheck":
-            actual = re.sub(rb"nofile:0:0: information: Active checkers.*\n", b"", actual)
+            actual = re.sub(rb"\nnofile:0:0: information: Active checkers.*\n", b"\n", actual)
         retcode = sp_child.returncode
         utils.assert_equal(target_output, actual)
         assert target_retcode == retcode