Make python version on poetry.dependencies less restrictive

[jymchng]

Hi, this is a beautiful template that I'm sure many of us are grateful for.

One issue though, would you mind changing the python version dependency on poetry.dependencies in pyproject.toml, i.e. https://github.com/BrianPugh/python-template/blob/main/pyproject.toml#L30, to be less restrictive?

Instead of ">=3.8", change it to "^3.8". This causes an issue as ">=3.8" is fundamentally different from "^3.8".

[BrianPugh]

>=3.8 means "anything more recent (inclusive) than python3.8, including python4 if it ever exists."

^3.8 means "anything more recent (inclusive) than python3.8, but less than python4."

I take the same opinion as Henry Shreiner in his blog post on upper bound version constraints. Namely, it generally just causes systemic issues to preemptively issue an upper bound version constraint on your library.