[CSV] don't apply string highlighting by default

CHANGELOG.md

@@ -11,6 +11,7 @@
 ## Syntaxes
 
 - Change the URL of Zig submodule from GitHub to Codeberg, see #3519 (@sorairolake)
+- Don't color strings inside CSV files, to make it easier to tell which column they belong to, see #3521 (@keith-hall)
 
 ## Themes