GentooImporter failing with InvalidVersion error

Error log:
```python
Failed to run vulnerabilities.importers.gentoo.GentooImporter: InvalidVersion("'3.24.48:3' is not a valid ")
Traceback (most recent call last):
File "/app/vulnerabilities/tasks.py", line 80, in legacy_runner
ImportRunner(run_class).run()
File "/app/vulnerabilities/import_runner.py", line 62, in run
count = self.process_advisories(advisory_datas=advisory_datas, importer_name=importer_name)
File "/app/vulnerabilities/import_runner.py", line 105, in process_advisories
for data in advisory_datas:
File "/app/vulnerabilities/importers/gentoo.py", line 41, in advisory_data
yield from self.process_file(file_path)
File "/app/vulnerabilities/importers/gentoo.py", line 69, in process_file
affected_packages = list(self.affected_and_safe_purls(child))
File "/app/vulnerabilities/importers/gentoo.py", line 108, in affected_and_safe_purls
VersionConstraint(version=GentooVersion(version), comparator="=").invert()
File "", line 7, in __init__
self.__attrs_post_init__()
File "/usr/local/lib/python3.9/site-packages/univers/versions.py", line 87, in __attrs_post_init__
raise InvalidVersion(f"{self.string!r} is not a valid {self.__class__!r}")
univers.versions.InvalidVersion: '3.24.48:3' is not a valid
```

See the run status here https://public.vulnerablecode.io/pipelines/vulnerabilities.importers.gentoo.GentooImporter/run/552198c1-4ed9-47d1-ab2c-1875f10ae74c/