[boost] Add support for libboost_python38.so filename format

Fixes #80
2 jobs for boost-conda-forge in 11 minutes and 39 seconds (queued for 1 second)
Status Name Job ID Coverage
  Build
passed build_linux_38 #245663
docker

00:08:06

75.0%
passed build_macos_intel_38 #245662
macos intel

00:11:39

76.0%