fix: keep behavior from v0.47 in PrepareProposal panic recovery

[facundomedica]

Description

In v0.47.x when recovering from a panic during PrepareProposal we return a proposal that includes all the transactions that it got from RequestPrepareProposal. This was later modified (without a clear reason afaik, maybe just by mistake).

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[github-actions]

@facundomedica your pull request is missing a changelog!

[julienrbrt]

Shouldn't we not do the same L463 as well then?
https://github.com/cosmos/cosmos-sdk/pull/17930/files#diff-389d02f089ab55575400f5300d3c5cfe277fde5f04bd0fe6a85456a7252d1099R463

[odeke-em]

Thanks @facundomedica! To lock in this behavior and ensure that it doesn't regress, let's add a regression test in which prepareProposal intentionally panics and then the regression test should confirm that the response has the set Txs as well as the error and the desired panic message. If we had that test in the first place, this would have been tightly flagged.

[facundomedica]

@odeke-em added a test, please check now

[odeke-em]

LGTM, thank you @facundomedica. I realize we can't check directly against the message but the regression test suffices to capture that even on intentional panics, we send back the Txs