[elpa] externals/xr updated (6200de8ccd -> f51db5fffe)

[ELPA Syncer]

elpasync pushed a change to branch externals/xr.

      from  6200de8ccd Run CI on release-snapshot (to become Emacs 29) as well
       new  b8141733cc Rearrange tests of xr-lint for character alternatives
       new  56f2dbab08 Add lint check for [A-z] etc
       new  f51db5fffe Fix xr-pp-rx-to-str tests in Emacs 30


Summary of changes:
 README     |  7 +++++++
 xr-test.el | 48 +++++++++++++++++++++++++++++-------------------
 xr.el      | 16 +++++++++++++---
 3 files changed, 49 insertions(+), 22 deletions(-)