test/py: Add pycryptodomex to list of required pakages

We wish to use pycryptodomex to verify code paths involving ECDSA
signatures. Add it to requirements.txt so that they get picked up
automatically .gitlab and .azure tasks

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

test/py/requirements.txt

@@ -10,6 +10,7 @@ packaging==19.2
 pbr==5.4.3
 pluggy==0.13.0
 py==1.8.0
+pycryptodomex==3.9.8
 pyelftools==0.27
 pygit2==0.28.2
 pyparsing==2.4.2