biology/py-crossmap: Fix build with Python 3.8+

* Add missing dependency devel/py-nose that is required to build.  With
  Python 3.6/3.7 there are no build issues because the sdist contains
  Python Eggs of "nose" for these versions.

While I'm here:

* Set NO_ARCH because the port has no architecture specific files.
* Make it concurrent safe, package installs a script and bump
  PORTREVISION due package change.

PR:		253815
Approved by:	portmgr (build fix)
MFH:		No (The port was added after the 2021Q1 branch)