Support mkdocs 1.6

[intentionally-left-nil]

Right now it's not possible to use mkdocs-techdocs-core and mkdocs 1.6, due to the very tight versioning coupling of mkdocs-material.

mkdocs-material needs to be bumped to 9.5.19 in order to allow (and sadly, require) mkdocs 1.6

[intentionally-left-nil]

Super cool that your github actions auto-close PR's.... maybe pinging reviewers to look at them would be better instead

[jonesbusy]

+1 here