Fix gevent and greenlet build issue

The gevent and greelet versions pinned in Odoo's requirements.txt
don't build anymore with the latest cython,
so we use the latest versions which have wheels.

Dockerfile

@@ -111,7 +111,12 @@ ARG odoo_version
 # Install Odoo requirements (use ADD for correct layer caching).
 # We use requirements from OCB for easier maintenance of older versions.
 ADD https://raw.githubusercontent.com/OCA/OCB/$odoo_version/requirements.txt /tmp/ocb-requirements.txt
-RUN pip install --no-cache-dir \
+# The sed command is to use the latest version of gevent and greenlet. The
+# latest version works with all versions of Odoo that we support here, and the
+# oldest pinned in Odoo's requirements.txt don't have wheels, and don't build
+# anymore with the latest cython.
+RUN sed -i -E "s/^(gevent|greenlet)==.*/\1/" requirements.txt \
+ && pip install --no-cache-dir \
       -r /tmp/ocb-requirements.txt \
       packaging