Temporarily downgrade sphinxcontrib-needs

As lfdocs-conf falsy forces 0.5.6 [1], we must temporarily
downgrade the version till lfdocs-conf is fixed.

[1] https://gerrit.linuxfoundation.org/infra/c/releng/docs-conf/+/70536

Issue-ID: DOC-782

Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>
Change-Id: Ie4ddd50c49290bbbf4bd8fa8a9a4f5e5878db93b
1 file changed