Enable syncing of docs

The docs job is failing in https://review.opendev.org/671840 and thus
nothing is synced in from openstack-ansible-tests. The failure is due to
the removal of entries from doc/requirements.txt. Add those
to test-requirements.txt instead.

Change-Id: I21bcbde8acc8d4fd83b28026bcec33f388e69912

doc/requirements.txt

@@ -8,5 +8,3 @@ sphinxcontrib-svg2pdfconverter>=0.1.0 # BSD
 openstackdocstheme>=2.0.0 # Apache-2.0
 doc8>=0.6.0 # Apache-2.0
 reno>=2.5.0 # Apache-2.0
-Jinja2>=2.10 # BSD License (3 clause)
-lxml!=3.7.0,>=3.4.1 # BSD

test-requirements.txt

@@ -0,0 +1,6 @@
+# These are actually only used for doc building but
+# doc/requirements.txt is synced from openstack-ansible-tests, so we
+# need to add them elsewhere.
+
+Jinja2>=2.10 # BSD License (3 clause)
+lxml!=3.7.0,>=3.4.1 # BSD

tox.ini

@@ -34,6 +34,7 @@ setenv =
 deps =
   -c{env:TOX_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt}
   -r{toxinidir}/doc/requirements.txt
+  -r{toxinidir}/test-requirements.txt
 commands =
     bash -c "rm -rf doc/build"
     # NOTE(mhayden): doc8 really dislikes the automated docs. This should be