test: 1.4.18 get xapian working under github actions and python 3.13 issue2551338 xapian doesn't build in CI for 3.13 python binary search for working version of xapian tarball. try 1.4.18 which may compile but not find proper headers or create output files with incorrect filetypes. 1.4.19 failed with: xapian_wrap.cc:65031:116: error: ‘FLAG_NO_POSITIONS’ is not a member of ‘Xapian::QueryParser’ [skip travis]