Fix group wiki inaccessible after deleting and creating group with the same name

What does this MR do and why?

This MR expires group wiki repository cache after getting Gitlab::Git::Repository::NoRepository in response to accessing the wiki repository through Gitaly.

This fixes a bug, where a group is deleted and then recreated with the same name, and the new wiki repository is inaccessible until the cache expires.

References

• Group Wiki inaccessible after group recreation ... (#560188 - closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Create a group.
2. Create a wiki page in that group's wiki to create a wiki repository.
3. Permanently delete the group.
4. Create a group with the same name, and access a new (now empty) wiki normally.

MR acceptance checklist

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