[ML] Unmute Inference Test

We believe elastic#136747 fixed this test and/or the test was transitory and is
now fixed.

Author: prwhelan

muted-tests.yml

@@ -250,9 +250,6 @@ tests:
 - class: org.elasticsearch.xpack.esql.action.CrossClusterCancellationIT
   method: testCancelSkipUnavailable
   issue: https://github.com/elastic/elasticsearch/issues/134865
-- class: org.elasticsearch.xpack.ml.integration.InferenceIT
-  method: testInferRegressionModel
-  issue: https://github.com/elastic/elasticsearch/issues/133603
 - class: org.elasticsearch.reservedstate.service.RepositoriesFileSettingsIT
   method: testSettingsApplied
   issue: https://github.com/elastic/elasticsearch/issues/126748