test: py: add pygit2 and pyelftools to requirements.txt

Add pygit2 and pyelftools to the list of packages for virtualenv
needed to run all sets of pytests.This fixes warnings like:

binman.elf_test.TestElf.testDecodeElf (subunit.RemotedTestCase):
Python elftools not available

Signed-off-by: Igor Opaniuk <igor.opaniuk@foundries.io>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/test/py/requirements.txt b/test/py/requirements.txt
index cf25118..926bcca 100644
--- a/test/py/requirements.txt
+++ b/test/py/requirements.txt
@@ -10,6 +10,8 @@
 pbr==5.4.3
 pluggy==0.13.0
 py==1.8.0
+pyelftools==0.27
+pygit2==1.4.0
 pyparsing==2.4.2
 pytest==5.2.1
 python-mimeparse==1.6.0