bug#64803: python-shiboken-6 fails

[Formbi]

Hi!

The package python-shiboken-6 fails with this error:

*** Error compiling 'signature_bootstrap.py'...
Sorry: IndentationError: unexpected indent (signature_bootstrap.py, line 64)

The line in question (and the neighboring ones for context) looks like this:

import base64
import importlib
        import importlib.machinery as imachi
import io
import sys
import traceback
import zipfile

I tried adding this to the package definition, but it didn't help:
(add-before 'build 'remove-indent
            (lambda _
              (substitute* 
"sources/shiboken6/libshiboken/embed/signature_bootstrap.py"
                           (("        import importlib.machinery as imachi")
                            "import importlib.machinery as imachi"))))

Someone on IRC suggested to use this, but it didn't work either:
(add-before 'build 'remove-indent
                        (lambda _
                          (substitute* 
"libshiboken/embed/signature_bootstrap.py"
                                       (("[ \t]*(import
               importlib\\.machinery.*)" _ suffix) suffix))))

How should I go about fixing this?

Kind regards