chore: pin msgpack to 0.5.6

Signed-off-by: Kim Ebert <kim@indicio.tech>

Author: KimEbert42

setup.py

@@ -108,7 +108,7 @@ def run(self):
                         # Pinned because of changing size of `crypto_sign_SECRETKEYBYTES` from 32 to 64
                         'libnacl==1.6.1',
                         # 'msgpack-python==0.5.6',
-                        'msgpack',
+                        'msgpack==0.5.6',
                         # 'orderedset==2.0.3',
                         'orderedset',
                         # 'packaging==20.9',