CLN: Simplify the type promote conditions in combine

Author: Licht-T

pandas/core/frame.py

@@ -4881,13 +4881,11 @@ def combine(self, other, func, fill_value=None, overwrite=True):
                     pass
             else:
                 # if we have different dtypes, possibly promote
-                new_dtype = this_dtype
-                if not is_dtype_equal(this_dtype, other_dtype):
-                    new_dtype = find_common_type([this_dtype, other_dtype])
-                    if not is_dtype_equal(this_dtype, new_dtype):
-                        series = series.astype(new_dtype)
-                    if not is_dtype_equal(other_dtype, new_dtype):
-                        otherSeries = otherSeries.astype(new_dtype)
+                new_dtype = find_common_type([this_dtype, other_dtype])
+                if not is_dtype_equal(this_dtype, new_dtype):
+                    series = series.astype(new_dtype)
+                if not is_dtype_equal(other_dtype, new_dtype):
+                    otherSeries = otherSeries.astype(new_dtype)
 
             # see if we need to be represented as i8 (datetimelike)
             # try to keep us at this dtype