python-congressclient fails to create SRPM due to unescaped nested macros.

[python-congressclient (master)]$ fedpkg srpm
error: Cannot use %python if %__python wasn't redefined to something other than /usr/bin/python.
error: lua script failed: [string "<lua>"]:4: error expanding macro
error: .../python-debtcollector/python-congressclient.spec: line 8: Macro %pyver_sitelib failed to expand
error: query of specfile .../python-congressclient/python-congressclient.spec failed, can't parse

Could not execute srpm: Could not get n-v-r-e from .../python-congressclient/python-congressclient.spec


Possible fix is at https://src.fedoraproject.org/rpms/python-debtcollector/pull-request/3

Alternate fix is also described there.

This blocks the Python 3.9 rebuild.