docs: Fix typo (#8785) — thanks, @zacharywelch!

Author: zacharywelch

docs/pages/product/data-modeling/concepts/calculated-members.mdx

@@ -93,7 +93,7 @@ FROM (
 ## Proxy dimensions
 
 **Proxy dimensions reference dimensions from the same cube or other cubes.**
-Proxy dimensions are convenient for reusing existing dimensions when definiting
+Proxy dimensions are convenient for reusing existing dimensions when defining
 new ones.
 
 ### Members of the same cube