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