test: refactor: Use absolute include paths for test data files
Summary:
Partial backport od core PR11651 (commit 138016b)
https://github.com/bitcoin/bitcoin/pull/11651/commits/138016bf9275692995d37f707e5b83e0d7fed1a9
Test Plan:
make check ninja check
Reviewers: #bitcoin_abc, deadalnix, jasonbcox
Reviewed By: #bitcoin_abc, jasonbcox
Differential Revision: https://reviews.bitcoinabc.org/D2969