avoid implicit string concatenation in rcs_stats.py

Co-authored-by: Copilot <[email protected]>

Author: mahf708

components/eamxx/cime_config/SystemTests/rcs_stats.py

@@ -762,7 +762,7 @@ def run_stats_comparison(
         comments.extend([
             "",
             f"Magnitude Threshold: {MAGNITUDE_THRESHOLD}",
-            "  (Minimum relative difference required for practical "
+            "  (Minimum relative difference required for practical ",
             "significance)",
         ])