Pin `mkdocs-material` version to force installing a newer version

[kabilar]

Description

• Currently, the mkdocs-deploy-gh-pages GitHub Action has an older version of mkdocs-material installed since it uses an older base image in the Dockerfile (i.e. version 9.0.6).
• This has caused a recent merge in this repository to fail in deploying. See failed run. See reference in the GitHub Actions run to mkdocs-material version 9.0.6 install. The recent merge is looking for an asset (i.e. X-Twitter logo) that was added in a newer version of mkdocs-material.
• Fix #118

Changes

• The changes proposed pin the mkdocs-material package to >= the latest version (i.e. version 9.5.10) so that the GitHub Actions are forced to install a newer version.

[yarikoptic]

Thank you for digging. Let's see...

[kabilar]

Thanks for merging. This issue looks to be resolved as the GitHub Action successfully deployed the site. Next, I will work on a GitHub Action to test the build before merging.

[yarikoptic]

are you sure you want an action instead of integration with RTD?

[kabilar]

I am not too familiar with the features/deployment of RTD, so I will have to look into it.