ci: Fix upgrade setup for nightly interchaintest runs.

[fastfadingviolets]

Description

We need to account for upgrade names now being the full version name, as well as provide a real upgrade name when running a nightly build. From now, nightly builds will use either the latest released version as their upgrade name--i.e. assuming that main is just building on top of that release--or will use vNext.0.0 if main has been updated to be a new major version.

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