Disable probabilistic sampling for test builds

Test builds sample so few sequences that probabilistic subsampling can
end up picking too few sequences for augur refine to work properly. This
commit disables probabilistic sampling for those builds.

tests/builds/tb/Snakefile

@@ -49,6 +49,7 @@ rule filter:
             --exclude {input.exclude} \
             --group-by {params.group_by} \
             --sequences-per-group {params.sequences_per_group} \
+            --no-probabilistic-sampling
         """
 
 rule mask:

tests/builds/various_export_settings/base.snakefile

@@ -50,6 +50,7 @@ rule filter:
             --output {output.sequences} \
             --group-by {params.group_by} \
             --sequences-per-group {params.sequences_per_group} \
+            --no-probabilistic-sampling \
             --min-date {params.min_date}
         """
 
@@ -112,4 +113,3 @@ rule refine:
             --date-inference {params.date_inference} \
             --clock-filter-iqd {params.clock_filter_iqd}
         """
-