🔧 Keep urllib3 below v2 in tests for compat

This is needed because `requests-unixsocket` is currently incompatible
with the new release stream of `urllib3`[[1]] and it's unclear how
long it will take to get the bugfix PR[[2]] merged and a release
published.

[1]: msabramo/requests-unixsocket#70
[2]: msabramo/requests-unixsocket#69

requirements/tests.in

@@ -56,3 +56,9 @@ trustme>=0.4.0
 
 # cryptography >= 3.4 started using Rust but it's unstable w/ old PyPy
 cryptography < 3.4; implementation_name == "pypy" and python_version < "3.8"
+
+# requests-unixsocket is currently incompatible with urllib3 v2
+# Refs:
+# * https://github.com/msabramo/requests-unixsocket/issues/70
+# * https://github.com/msabramo/requests-unixsocket/pull/69
+urllib3 < 2