Fix raw string in cohort_diversity_stats error message

Replace r"..." with f"..." so the cohort value is interpolated
into the TypeError message instead of showing a literal placeholder.

Signed-off-by: suhr25 <suhridmarwah07@gmail.com>

Author: suhr25

malariagen_data/anopheles.py

@@ -1066,7 +1066,7 @@ def cohort_diversity_stats(
             cohort_label, cohort_query = cohort
 
         else:
-            raise TypeError(r"invalid cohort parameter: {cohort!r}")
+            raise TypeError(f"invalid cohort parameter: {cohort!r}")
 
         debug("access allele counts")
         ac = self.snp_allele_counts(