Update python dependency and enable Dependabot for Dockerfile

[sebbo2002]

I use the pyatv Docker container for building the pyatv-mqtt-bridge container. Due to that, I noticed that the Alpine image as well as the Python version used for the pyatv image is comparatively old.

I updated the Python base image from 3.9.7 to 3.11.4 and also enabled Dependabot for the Dockerfile, so that the base image is kept up to date. Hope it works, I don't know anything about Python so I didn't even try it.

Thanks 👋🏼

[postlund]

Sorry about the delay 😞 But thanks, this makes a lot of sense! Newer is always better (and everything is better with bacon)!

[codecov[bot]]

Codecov Report

Patch coverage has no change and project coverage change: -0.15% :warning:

Comparison is base (84d8222) 88.70% compared to head (04d6d98) 88.56%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2146 +/- ## ========================================== - Coverage 88.70% 88.56% -0.15% ========================================== Files 163 163 Lines 11070 11070 ========================================== - Hits 9820 9804 -16 - Misses 1250 1266 +16 ``` [see 3 files with indirect coverage changes](https://app.codecov.io/gh/postlund/pyatv/pull/2146/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pierre+St%C3%A5hl)

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