[bitcoin/bitcoin] Don’t edit Chainparams after initialization (#13311)

promag commented on this pull request.

> {
— globalChainParams->UpdateVersionBitsParameters(d, nStartTime, nTimeout);
+ SelectBaseParams(network);
+ globalChainParams = CreateChainParams(network, gArgs);

Tend to agree with @ajtowns.

> but the idea was that some unittests could create their own custom ArgsManager instead of using gArgs

If needed it can mutate gArgs? Or this can be done when needed?