Backport PR #41981 on branch 1.3.x (BLD: Update MANIFEST.in)
Backport PR #41981: BLD: Update MANIFEST.in
no idea why ci doesn't run. #41966 has been merged. when doing the same for 1.2.x, #38360 we also backported, so maybe is necessary

will be testing 1.3.x before release so merging this.