Remove upper Python version constraint

It was introduced for aioimaplib which was incompatible with newer
Python versions, but is no longer used.

pyproject.toml

@@ -29,7 +29,7 @@ dmarc-metrics-exporter = "dmarc_metrics_exporter.__main__:run"
 bite-parser = "^0.1.2"
 dataclasses-serialization = "^1.3.1"
 prometheus_client = "^0.11.0"
-python = "^3.7,<3.10"
+python = "^3.7"
 typing-extensions = "^4.0.1"
 uvicorn = {extras = ["standard"], version = "^0.15.0"}
 xsdata = "^21.9"