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)