Use assignment instead of annotation in third party enums (#11957)

stubs/fpdf2/fpdf/enums.pyi

@@ -77,8 +77,8 @@ class TableCellFillMode(CoerciveEnum):
     def should_fill_cell(self, i: int, j: int) -> bool: ...
 
 class TableSpan(CoerciveEnum):
-    ROW: Literal["ROW"]
-    COL: Literal["COL"]
+    ROW = "ROW"
+    COL = "COL"
 
 class TableHeadingsDisplay(CoerciveIntEnum):
     NONE = 0