Pin mkdocs-material>=9.7.0 to fix lunr.js global context error

This fixes the TypeError: can't access property 'console', e is undefined
error in the search worker when using Vietnamese and other locales.

See: ultrabug/mkdocs-static-i18n#313

Author: DavidMStraub

requirements.txt

@@ -1,5 +1,5 @@
 mkdocs
-mkdocs-material
+mkdocs-material>=9.7.0
 mkdocs-glightbox
 mkdocs-redirects
 mkdocs-static-i18n