Restrict to old enough paramiko on RHEL 8 or other systems using Pyth…

…on 3.6. (ansible-collections#563)

tests/utils/constraints.txt

@@ -12,6 +12,7 @@ cryptography >= 1.3.0, < 3.4 ; python_version < '3.6' # cryptography 3.4 drops s
 urllib3 < 1.24 ; python_version < '2.7' # urllib3 1.24 and later require python 2.7 or later
 wheel < 0.30.0 ; python_version < '2.7' # wheel 0.30.0 and later require python 2.7 or later
 paramiko < 2.4.0 ; python_version < '2.7' # paramiko 2.4.0 drops support for python 2.6
+paramiko < 3.0.0 ; python_version < '3.7' # paramiko 3.0.0 forces installation of a too new cryptography
 requests < 2.20.0 ; python_version < '2.7' # requests 2.20.0 drops support for python 2.6
 requests < 2.28 ; python_version < '3.7' # requests 2.28.0 drops support for python < 3.7
 virtualenv < 16.0.0 ; python_version < '2.7' # virtualenv 16.0.0 and later require python 2.7 or later