Hide <style> tags from Tidy
Some versions of html-tidy (e.g. the one currently in use on WMF wikis)
will try to move all <style> tags in the body into the head, effectively
removing them for our purposes. We need to avoid that for TemplateStyles.
Bug: T167349
Change-Id: I133776d16f366cad73ed30af0e5a665fdf9f5ed9