TEST-#7681: Interop Tests should all use Backend.get instead of "Ray" (#7680)

Missed a line in create_test_series_in_defined_mode where we want to get
the default Backend instead of "Ray"

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- [x] Resolves #7681
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Author: sfc-gh-jkew

modin/tests/pandas/native_df_interoperability/utils.py

@@ -45,6 +45,8 @@ def create_test_df_in_defined_mode(
 
     if not isinstance(native, bool):
         raise ValueError("`native` should be True or False.")
+
+    # Use the default backend unless native
     hybrid_backend = "Pandas" if native else Backend.get()
     with switch_to_native_execution() if native else nullcontext():
         with config_context(AutoSwitchBackend=False, Backend=hybrid_backend):
@@ -62,7 +64,8 @@ def create_test_series_in_defined_mode(
     if not isinstance(native, bool):
         raise ValueError("`native` should be True or False.")
 
-    hybrid_backend = "Pandas" if native else "Ray"
+    # Use the default backend unless native
+    hybrid_backend = "Pandas" if native else Backend.get()
     with switch_to_native_execution() if native else nullcontext():
         with config_context(AutoSwitchBackend=False, Backend=hybrid_backend):
             modin_ser, pandas_ser = create_test_series(