Fix Python 3.9 Tests (#284)

Co-authored-by: James Hilton-Balfe <50501825+Gobot1234@users.noreply.github.com>

pyproject.toml

@@ -12,7 +12,7 @@ packages = [
 ]
 
 [tool.poetry.dependencies]
-python = "^3.6"
+python = ">=3.6.2,<4.0"
 black = { version = ">=19.3b0", optional = true }
 dataclasses = { version = "^0.7", python = ">=3.6, <3.7" }
 grpclib = "^0.4.1"
@@ -21,7 +21,7 @@ python-dateutil = "^2.8"
 
 [tool.poetry.dev-dependencies]
 asv = "^0.4.2"
-black = "^20.8b1"
+black = "^21.11b0"
 bpython = "^0.19"
 grpcio-tools = "^1.30.0"
 jinja2 = "^2.11.2"