AttributeError: module 'icu' has no attribute 'Locale'

[Benjamin Drung]

I stumbled over this crash during import while I was working on the tzdata package update. How to reproduce: Install natsort, but do not install the icu Python module. Create an empty directory called `icu` and then try to import natsort:

```
$ sudo apt install python3-natsort
$ sudo apt remove python3-icu
$ mkdir icu
$ python3 -c "import natsort"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/python3/dist-packages/natsort/__init__.py", line 3, in <module>
    from natsort.natsort import (
  File "/usr/lib/python3/dist-packages/natsort/natsort.py", line 846, in <module>
    os_sort_key = os_sort_keygen()
                  ^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/natsort/natsort.py", line 814, in os_sort_keygen
    loc = natsort.compat.locale.get_icu_locale()
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/natsort/compat/locale.py", line 42, in get_icu_locale
    return cast(str, icu.Locale(".".join(getlocale())))
                     ^^^^^^^^^^
AttributeError: module 'icu' has no attribute 'Locale'
```

ProblemType: Bug
DistroRelease: Ubuntu 23.04
Package: python3-natsort 8.0.2-2
ProcVersionSignature: Ubuntu 6.2.0-20.20-generic 6.2.6
Uname: Linux 6.2.0-20-generic x86_64
ApportVersion: 2.26.1-0ubuntu2
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Sun May 7 00:37:52 2023
Dependencies:

InstallationDate: Installed on 2022-03-09 (423 days ago)
InstallationMedia: Ubuntu 21.10 "Impish Indri" - Release amd64 (20211012)
PackageArchitecture: all
SourcePackage: natsort
UpgradeStatus: Upgraded to lunar on 2023-04-25 (11 days ago)