Allow pytest 7 (#64)

Author: alex-treebeard

pyproject.toml

@@ -15,7 +15,7 @@ nbmake = "nbmake.pytest_plugin"
 
 [tool.poetry.dependencies]
 pydantic = "^1.7.2"
-pytest = "^6.1.0"
+pytest = ">=6.1.0"
 python = "^3.6.1"
 nbclient = "^0.5.5"
 nbformat = "^5.0.8"