[DNM] Testing docs bump with new Sphinx

Sphinx updates can be scary.  This change leverages a constraints bump to see what breaks.

Depends-On: https://review.opendev.org/c/openstack/requirements/+/916565
Change-Id: Ia49c128476ed1888ab9187d0de00c3d2ed355b09

doc/requirements.txt

@@ -1,2 +1,3 @@
 sphinx>=2.0.0,!=2.1.0 # BSD
 openstackdocstheme>=2.2.1 # Apache-2.0
+# Force docs rebuild: 

requirements.txt

@@ -5,3 +5,4 @@
 pbr!=2.1.0,>=2.0.0 # Apache-2.0
 
 diskimage-builder!=1.6.0,!=1.7.0,!=1.7.1,>=1.1.2 # Apache-2.0
+# Force requirements rebuild: 

setup.py

@@ -19,3 +19,5 @@ setuptools.setup(
     setup_requires=['pbr>=2.0.0'],
     py_modules=[],
     pbr=True)
+
+# Force unittests: