Use f-string to format log.warning message

The % format in this warning message was broken, and printed "%s" instead of a
path. This may be something to do with our interception and coloring of warning
messages, but I can't be sure.

The simplest fix is to use an f-string (as we do for other warnings), because
that results in the string being formatted before it is passed to logging.

Signed-off-by: John Pennycook <john.pennycook@intel.com>

Author: Pennycook

codebasin/config.py

@@ -499,7 +499,7 @@ def load_database(dbpath, rootdir):
         # Skip files that don't exist.
         # (e.g., because they're generated by running make)
         if not os.path.exists(path):
-            log.warning("Ignoring non-existent file: %s", path)
+            log.warning(f"Ignoring non-existent file: {path}")
             continue
 
         # Parse command-line arguments, emulating compiler-specific behavior.