test: reduce BRRHeight in regtest

[ogabrielides]

Issue being fixed or feature implemented

In regtest, Block Reward Reallocation is buried at height 2500, which happens after v20 activation.

What was done?

Reduced BRRHeight in regtest from 2500 to 1000. The purpose of this change is to simplify regtests of Platform as well. Note: This change affects only regtest.

How Has This Been Tested?

tests

Breaking Changes

no, this only affects Regtest (where we make no guarantees about breaking stuff)

Checklist:

• [x] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [x] I have added or updated relevant unit/integration/functional/e2e tests
• [ ] I have made corresponding changes to the documentation
• [x] I have assigned this pull request to a milestone (for repository code-owners and collaborators only)

[PastaPastaPasta]

doing:

./src/qt/dash-qt --testnet --reindex --assumevalid=0