Remove the conversion because it's already done in to_dataframe

Author: seisman

pygmt/clib/session.py

@@ -1765,16 +1765,10 @@ def return_table(
             return None
         # Read the virtual file as a GMT dataset and convert to pandas.DataFrame
         result = self.read_virtualfile(vfile, kind="dataset").contents.to_dataframe()
-        # assign column names
+        # Assign column names
         if column_names is not None:
             result.columns = column_names
-        # convert text data from object dtype to string dtype
-        result = result.convert_dtypes(
-            convert_string=True,
-            convert_integer=False,
-            convert_floating=False,
-            convert_boolean=False,
-        )
+        # Pandas.DataFrame output
         if output_type == "pandas":
             return result
         # NumPy.ndarray output