env: add upper version constraint for pytest to keep compatibility with python3.5

https://github.com/fphammerle/ical2vdir/pull/26/commits/e28ca1ced412e23083e7adc8d9a936a521c07e88

Pipfile

@@ -11,7 +11,7 @@ numpy = "<1.19.0"
 
 [dev-packages]
 pylint = "*"
-pytest = "*"
+#pytest = "*"
 pytest-cov = "*"
 pytest-timeout = "*"
 
@@ -22,6 +22,8 @@ importlib-metadata = {version = "<3", markers="python_version < '3.8'"}
 isort = "<5"
 # workaround https://github.com/pytest-dev/pytest/issues/3953
 pathlib2 = {version = "*", markers="python_version < '3.6'"}
+# https://github.com/pytest-dev/pytest/commit/179f4326df2b644f0ab73f78e4770dafcbdcd89f#diff-fa602a8a75dc9dcc92261bac5f533c2a85e34fcceaff63b3a3a81d9acde2fc52R52
+pytest = "<6.2"
 # https://github.com/jaraco/zipp/commit/05a3c52b4d41690e0471a2e283cffb500dc0329a
 zipp = "<2"
 

Pipfile.lock

@@ -1,7 +1,7 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "22cf82d03532bc962e00557bfaec45e6a3ec033bbada1f6c94fed2a6a3ed8507"
+            "sha256": "d6f22fde3dc0c59173a2f2fe7651e69cec3ba0ed9f88222f5db4c6440ce676a1"
         },
         "pipfile-spec": 6,
         "requires": {