kunit: fix missing f in f-string in run_checks.py

We're missing the `f` prefix to have python do string interpolation, so
we'd never end up printing what the actual "unexpected" error is.

Fixes: ee92ed3 ("kunit: add run_checks.py script to validate kunit changes")
Signed-off-by: Daniel Latypov <dlatypov@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

Author: dlatypov

tools/testing/kunit/run_checks.py

@@ -61,7 +61,7 @@ def main(argv: Sequence[str]) -> None:
 		elif isinstance(ex, subprocess.CalledProcessError):
 			print(f'{name}: FAILED')
 		else:
-			print('{name}: unexpected exception: {ex}')
+			print(f'{name}: unexpected exception: {ex}')
 			continue
 
 		output = ex.output