fix: make mkdocs-serve should work with no mkdocs installed [skip ci]

[rfay]

The Issue

@mandrasch reported in https://discord.com/channels/664580571770388500/1124990159629320262/1124990159629320262 that he couldn't use the local make mkdocs-serve

How This PR Solves The Issue

Revert to explicit older docker version for mkdocs.

Manual Testing Instructions

Run make mkdocs-serve without mkdocs installed locally.

[tyler36]

Confirmed fixed.

I do not have mkdocs installed locally (WSL), so the command was falling back to docker solution.
This was failing with the following error: stderr: 'fatal: detected dubious ownership in repository at '/docs

After explicitly setting mkdocs version to 1.2.3 in Makefile, it worked:

$ make mkdocs-serve 
...
INFO     -  Documentation built in 8.22 seconds
INFO     -  [03:02:24] Watching paths for changes: 'docs/content', 'mkdocs.yml'
INFO     -  [03:02:24] Serving on http://0.0.0.0:8000/en/latest/