Fix exception handling

[T-Kukawka]

Added handling of Github exception, as it started failing for repos with no changelog while running update-generated-content as:

Repo giantswarm/docs
Getting releases for giantswarm/docs
Traceback (most recent call last):
  File "/workdir/script.py", line 333, in <module>
    changelog = get_changelog_file(g, repo_short)
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/workdir/script.py", line 56, in get_changelog_file
    remote_file = repo.get_contents('CHANGELOG.md')
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/github/Repository.py", line 2151, in get_contents
    headers, data = self._requester.requestJsonAndCheck(
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/github/Requester.py", line 494, in requestJsonAndCheck
    return self.__check(*self.requestJson(verb, url, parameters, headers, input, self.__customConnection(url)))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/github/Requester.py", line 525, in __check
    raise self.createException(status, responseHeaders, data)
github.GithubException.GithubException: 404 {"message": "No object found for the path CHANGELOG.md", "documentation_url": "https://docs.github.com/v3/repos/contents/", "status": "404"}
make: *** [Makefile:25: changes] Error 1

Successful action run: https://github.com/giantswarm/docs/pull/2461/files

[github-actions]

This PR moves/renames or deletes some files. Please make sure to

• maintain references (also important for images)
• Maintain aliases in the front matter of moved markdown files