Unmute FieldSortIT testSortMixedFieldTypes (#137724)

This test is most likely fixed by #136889.

Author: cbuescher

muted-tests.yml

@@ -372,9 +372,6 @@ tests:
 - class: org.elasticsearch.xpack.test.rest.XPackRestIT
   method: test {p0=analytics/nested_top_metrics_sort/terms order by top metrics numeric not null integer values}
   issue: https://github.com/elastic/elasticsearch/issues/135162
-- class: org.elasticsearch.search.sort.FieldSortIT
-  method: testSortMixedFieldTypes
-  issue: https://github.com/elastic/elasticsearch/issues/129445
 - class: org.elasticsearch.gradle.TestClustersPluginFuncTest
   method: override jdk usage via ES_JAVA_HOME for known jdk os incompatibilities
   issue: https://github.com/elastic/elasticsearch/issues/135413