Github workflow for `go mod tidy`

[rootulp]

Context

https://github.com/celestiaorg/celestia-core/pull/871#discussion_r1006982465

Problem

It is possible for a PR to be merged to this repo where go mod tidy hasn't been run. This is problematic because when developers pull latest v0.34.x-celestia and make a change, running go mod tidy may modify imports in go.mod that are unrelated to their change.

Proposal

Add a Github workflow that fails if go mod tidy hasn't been run on the PR