Add GDScript .editorconfig rules

- Uniformize `.gd` unit test files indentation to tabs (where needed)

modules/gdscript/tests/scripts/runtime/errors/constant_dictionary_erase.gd

@@ -1,4 +1,4 @@
 const dictionary := {}
 
 func test():
-  dictionary.erase(0)
+	dictionary.erase(0)

modules/gdscript/tests/scripts/runtime/features/array_string_stringname_equivalent.gd

@@ -9,7 +9,7 @@ func test():
 	array_sname.push_back(&"godot")
 	print("String in Array: ", "godot" in array_sname)
 
-  # Not equal because the values are different types.
+	# Not equal because the values are different types.
 	print("Arrays not equal: ", array_str != array_sname)
 
 	var string_array: Array[String] = []

modules/gdscript/tests/scripts/runtime/features/dictionary_string_stringname_equivalent.gd

@@ -13,5 +13,5 @@ func test():
 	print("String gets StringName: ", stringname_dict.get("abc"))
 
 	stringname_dict[&"abc"] = 42
-  # They compare equal because StringName keys are converted to String.
+	# They compare equal because StringName keys are converted to String.
 	print("String Dictionary == StringName Dictionary: ", string_dict == stringname_dict)

modules/gdscript/tests/scripts/runtime/features/parameter_shadowing.gd

@@ -3,23 +3,23 @@
 var a: int = 1
 
 func shadow_regular_assignment(a: Variant, b: Variant) -> void:
-  print(a)
-  print(self.a)
-  a = b
-  print(a)
-  print(self.a)
+	print(a)
+	print(self.a)
+	a = b
+	print(a)
+	print(self.a)
 
 
 var v := Vector2(0.0, 0.0)
 
 func shadow_subscript_assignment(v: Vector2, x: float) -> void:
-  print(v)
-  print(self.v)
-  v.x += x
-  print(v)
-  print(self.v)
+	print(v)
+	print(self.v)
+	v.x += x
+	print(v)
+	print(self.v)
 
 
 func test():
-  shadow_regular_assignment('a', 'b')
-  shadow_subscript_assignment(Vector2(1.0, 1.0), 5.0)
+	shadow_regular_assignment('a', 'b')
+	shadow_subscript_assignment(Vector2(1.0, 1.0), 5.0)