i18n: Add new markup for lazy translation of giphy ratings.

Also, it adds phrases such as 'rated Y' to the ignored list.
Otherwise, the linter would require to write it as 'rated y'.

tools/lib/capitalization.py

@@ -106,6 +106,12 @@ IGNORED_PHRASES = [
     r"your-organization-url",
     # Used in invite modal
     r"or",
+    # Used in GIPHY integration setting. GIFs Rating.
+    r"rated Y",
+    r"rated G",
+    r"rated PG",
+    r"rated PG13",
+    r"rated R",
     # Used in GIPHY popover.
     r"GIFs",
     r"GIPHY",