Add space after period in ToC warning (#776)

src/furo/assets/styles/components/_table_of_contents.sass

@@ -58,4 +58,4 @@
   color: var(--color-problematic)
   background: rgba(255, 0, 0, 0.25)
   &::before
-    content: "ERROR: Adding a table of contents in Furo-based documentation is unnecessary, and does not work well with existing styling.Add a 'this-will-duplicate-information-and-it-is-still-useful-here' class, if you want an escape hatch."
+    content: "ERROR: Adding a table of contents in Furo-based documentation is unnecessary, and does not work well with existing styling. Add a 'this-will-duplicate-information-and-it-is-still-useful-here' class, if you want an escape hatch."