chore(api/core): apply ruff reformatting (#7624)

api/core/app/segments/variables.py

@@ -23,11 +23,11 @@ class Variable(Segment):
     """
 
     id: str = Field(
-        default='',
+        default="",
         description="Unique identity for variable. It's only used by environment variables now.",
     )
     name: str
-    description: str = Field(default='', description='Description of the variable.')
+    description: str = Field(default="", description="Description of the variable.")
 
 
 class StringVariable(StringSegment, Variable):
@@ -62,7 +62,6 @@ class ArrayObjectVariable(ArrayObjectSegment, Variable):
     pass
 
 
-
 class SecretVariable(StringVariable):
     value_type: SegmentType = SegmentType.SECRET