Properly set the tox pandas value

Author: smlindauer

tox.ini

@@ -46,7 +46,7 @@ deps =
     tests: betamax >= 0.8.1
     tests: betamax_serializers >= 0.2.0
     tests: scikit-learn
-    tests: pandas == 1.5.3
+    tests: pandas < 2.0.0
     tests: cython               # required to install pandas from source
     tests: swat >= 1.8
     tests: kerberos ; platform_system != "Windows" and platform_system != "Darwin"