comanage-registry:3.2.1-internet2-tier-1 container image build fails when installing supervisor with an upgraded pip

As of commit 18645beb8708b8cc1a505c0339bb78a2b194df42 of https://github.internet2.edu/docker/comanage-registry-docker/ (HEAD at the time of this incident), the COmanage container build process is failing on the comanage-registry:3.2.1-internet2-tier-1 image.  It looks like comanage-registry-docker/comanage-registry-internet2-tier/Dockerfile tries to install the supervisor Python package after upgrading the system-provided pip but fails with the following error:
Traceback (most recent call last):
File "/usr/bin/pip", line 9, in <module>
load_entry_point('pip==21.0.1', 'console_scripts', 'pip')()
File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 378, in load_entry_point
return get_distribution(dist).load_entry_point(group, name)
File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 2566, in load_entry_point
return ep.load()
File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 2260, in load
entry = _import_(self.module_name, globals(),globals(), ['__name__'])
File "/usr/lib/python2.7/site-packages/pip/_internal/cli/main.py", line 60
sys.stderr.write(f"ERROR: {exc}")
^
SyntaxError: invalid syntax
Removing the pip install -U pip command that modifies the base operating system fixes this problem and allows the container build process to complete.