The _giscanner module depends on the ABI version used during the build:

https://build.opensuse.org/package/live_build_log/openSUSE:Factory:Staging:C/gobject-introspection/standard/x86_64

[  108s]  /usr/lib64/gobject-introspection/giscanner/__init__.py 0 (none)
100644 root root 0 4294967295 
[  108s]
-/usr/lib64/gobject-introspection/giscanner/_giscanner.cpython-38-x86_64-linux-gnu.so
0 (none) 100755 root root 0 4294967295 
[  108s]
+/usr/lib64/gobject-introspection/giscanner/_giscanner.cpython-37m-x86_64-linux-gnu.so
0 (none) 100755 root root 0 4294967295 
[  108s]  /usr/lib64/gobject-introspection/giscanner/_version.py 0 (none)
100644 root root 0 4294967295 

Trying to use g-ir-scanner then leads to non-obvious errors, e.g.:

https://build.opensuse.org/build/openSUSE:Factory:Staging:C/standard/x86_64/fcitx/_log

[   50s] [ 28%] Built target fcitx-addon-fcitx-classic-ui--headers-1
[   50s] Scanning dependencies of target fcitx-addon-fcitx-x11--addon--conf-1
[   50s] Traceback (most recent call last):
[   50s]   File "/usr/bin/g-ir-scanner", line 98, in <module>
[   50s]     from giscanner.scannermain import scanner_main
[   50s]   File "/usr/lib64/gobject-introspection/giscanner/scannermain.py",
line 35, in <module>
[   50s]     from giscanner.ast import Include, Namespace
[   50s]   File "/usr/lib64/gobject-introspection/giscanner/ast.py", line 29,
in <module>
[   50s]     from .sourcescanner import CTYPE_TYPEDEF, CSYMBOL_TYPE_TYPEDEF
[   50s]   File "/usr/lib64/gobject-introspection/giscanner/sourcescanner.py",
line 33, in <module>
[   50s]     from giscanner._giscanner import SourceScanner as CSourceScanner
[   50s] ModuleNotFoundError: No module named 'giscanner._giscanner'