Update middleman to 4.4.2 to receive build performance increase

Why is this change being made?

As described in #12405 (closed), I was able to shave off over a minute on the handbook build time by resolving an upstream regular expression issue. This should hopefully help with local build times as well as removing unnecessary CPU cycles in pipelines. :)

Why not wait for the next release of middleman? New releases are fairly infrequent, so accepting this MR would depend if you think it's worth using a GitHub ref for the performance improvement or not in the meantime.

edit: The new release of middleman is now available (4.4.2). This MR runs bundle update middleman

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Closes #12405 (closed)