cli: Fix multisig error message spacing #35617

This fixes a small user-facing error-message typo in bitcoin-tx.

When outmultisig is given mismatched parameters, the current error joins the number of keys and "signatures" without a space, e.g. Required 4 of 3signatures.

The change also adds coverage alongside the existing malformed outmultisig cases in bitcoin-util-test.json.

Tested:

• python3 -m json.tool test/functional/data/util/bitcoin-util-test.json
• git diff --cached --check

Not run:

• test/functional/test_runner.py tool_utils.py, because cmake is not installed in this environment and there is no configured build directory.

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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35617.

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This is an extremely small typo fix which we usually discourage since every PR review requires so much human and CI resources. But I also want to flag this

cmake is not installed in this environment and there is no configured build directory.

Sounds like PR was written by an LLM without any human understanding.

I recommend closing this PR and finding more productive ways to contribute to the project.

lgtm ACK cd6f4e9a6f981cce22c0ffa77cfa914d3bf7f2db

Seems fine to fix a typo and add coverage.

cc @m3dwards Looks like corecheck does not include bitcoin-util coverage, and maybe it should be added?