Merge bitcoin#740: Make recovery/main_impl.h non-executable

ffef45c Make recovery/main_impl.h non-executable (Elichai Turkel)

Pull request description:

  Opened it because of bitcoin#18650

  I assume it doesn't matter?
  But because I'm not sure I preferred to open this then let the info go away in case someone thinks it does matter.

ACKs for top commit:
  real-or-random:
    ACK ffef45c

Tree-SHA512: 381aed7f99fd739f4059b2e526ba9cd75b55b4fa86c9cc040fbf6b93055ce8558cc69c4ccf5d8a422b17022ca376cc9a608cf5af8d5841d62c5953f40825f5ff

Author: real-or-random