Move pytest-subtests to dev

Author: Steve Ayers

Pipfile

@@ -6,10 +6,10 @@ name = "pypi"
 [packages]
 cel-python = "==0.2.*"
 protobuf = "==6.*"
-pytest-subtests = "*"
 
 [dev-packages]
 pytest = "*"
+pytest-subtests = "*"
 mypy = "*"
 ruff = "*"
 types-protobuf = "==6.30.2.20250503"