fix: Add min_cohort_size=0 to variant_query test for amin1_sim compatibility

For amin1_sim (single-sampleset with few samples), the default
min_cohort_size=10 filters out all cohorts, raising ValueError before
the variant_query path is reached. This prevents the expected
UserWarning from being emitted, causing the test to fail with
'DID NOT WARN'. Setting min_cohort_size=0 ensures cohorts are
available so the variant query empty-result warning can be tested.

Author: khushthecoder

tests/anoph/test_snp_frq.py

@@ -1529,6 +1529,7 @@ def test_allele_frequencies_advanced_with_variant_query(
             area_by=area_by,
             period_by=period_by,
             variant_query=variant_query,
+            min_cohort_size=0,
         )
         assert ds_snp.sizes["variants"] == 0
 
@@ -1539,6 +1540,7 @@ def test_allele_frequencies_advanced_with_variant_query(
             area_by=area_by,
             period_by=period_by,
             variant_query=variant_query,
+            min_cohort_size=0,
         )
         assert ds_aa.sizes["variants"] == 0