bore: Ensure ignore_mask is always float

`ignore_mask` causes the following error if it's passed at 8bit:

```
VapourSynth encountered a fatal error: Filter  returned a frame that's not of the declared format
```

And silently crashes VS instead if it's neither 8bit nor float.

vsadjust/borders.py

@@ -3,7 +3,7 @@
 from itertools import chain
 from typing import Sequence
 
-from vstools import CustomEnum, CustomValueError, FunctionUtil, KwargsT, NotFoundEnumValue, PlanesT, core, vs
+from vstools import CustomEnum, CustomValueError, FunctionUtil, KwargsT, NotFoundEnumValue, PlanesT, core, depth, vs
 
 __all__ = [
     'bore'
@@ -58,6 +58,9 @@ def __call__(
                 'Invalid Bore enum!', func.func, dict(member=self, valid_function=bore.__members__.keys())
             )
 
+        if kwargs.get('ignore_mask', False):
+            kwargs['ignore_mask'] = depth(kwargs['ignore_mask'], func.bitdepth)  # type:ignore
+
         proc_clip: vs.VideoNode = func.work_clip
 
         for plane in func.norm_planes: