Add missing newline in util_ChainMerge test #17388

This was causing a lot of test cases not not be very meaningful because multiple configuration options were combined into one line.

The changes in test output with this fix make sense and look like:

- testnet=1 regtest=1 || test
+ testnet=1 regtest=1 || error: Invalid combination of -regtest, -testnet and -chain. Can use at most one.

Issue was reported and debugged by Wladimir J. van der Laan laanwj@protonmail.com in #17385 (comment)

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Thanks!

This shows the differences between the old and new test output : https://gist.github.com/laanwj/f3a436dd1d33d44f5a78d94bfa4ebcdb

Yes, makes a lot more sense now. ACK 3645e4ca0033bb6365f41ef710111780c139370f

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #16411 (Signet support by kallewoof)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

ACK 3645e4ca0033bb6365f41ef710111780c139370f -- diff looks correct