f59bbb61af test: Fix bug in blockfilter_index_tests. (Jim Posen)
Pull request description:
The test case tests a chain reorganization, however the two chains were generated in the same manner and thus produced the same blocks.
This issue was [pointed out](https://github.com/bitcoin/bitcoin/pull/14121#discussion_r334282663) by MarcoFalke.
ACKs for top commit:
MarcoFalke:
Thanks! ACK f59bbb61af (looked at the diff on GitHub, didn't compile, nor run tests)
Tree-SHA512: a2f063ae9312051ffc2a3fcc1116a6a8ac09beeef261bc40aa3ff7270ff4de22a790eb19fec6b15ba1eb46e78f1f317bfd91472d8581b95bb9441a56b102554e