build: Fix CustomTarget initializer annotation
the `output` parameter is a string, not an int.
@@ -2567,7 +2567,7 @@ class CustomTargetIndex(HoldableObject):
the sources.
"""
- def __init__(self, target: CustomTarget, output: int):
+ def __init__(self, target: CustomTarget, output: str):
self.typename = 'custom'
self.target = target
self.output = output
