Support for redis v7 (via `go-redis` upgrade)

[pat-s]

Feature Description

Redis v7 seems to require go-redis >= 9.0 as this version includes some important redis 7.0 fixes.

One of them is redis/go-redis#2110, which adds support for a connection string change in redis 7.0 which prevents from connection to redis-cluster instances of >= 7.0.

gitea 2023/04/13 20:00:47 routers/init.go:61:mustInit() [F] code.gitea.io/gitea/modules/cache.NewContext failed: got 4 elements in cluster info address, expected 2 or 3

The corresponding issue is redis/go-redis#2085 which then links to the PR mentioned above.
The current version in use is v8.11.5: https://github.com/go-gitea/gitea/blob/main/go.mod#L47

Screenshots

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