lang/python3(6|7|8|9|10|11): work around unwanted multiarch detection again

In ports 6bef09666460 we patched out python's erroneous multiarch
detection using sed, but upstream changed the surrounding parts in the
configure script to defeat the regex we were using. Update the regex to
cope with the change.

PR: 259896, 258377
MFH: 2021Q4
Approved by: maintainer timeout (9 days)