[web] Fix message search copy

Summary: Fix message search copy, as requested in https://linear.app/comm/issue/ENG-4398/fix-copy-for-web-message-search

Test Plan: Checked that the header of the message search modal now says "Search messages"

Reviewers: ashoat, michal

Reviewed By: michal

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D8516

web/modals/search/message-search-modal.react.js

@@ -128,7 +128,7 @@ function MessageSearchModal(props: ContentProps): React.Node {
   );
 
   return (
-    <Modal name="Search Message" onClose={popModal} size="large">
+    <Modal name="Search messages" onClose={popModal} size="large">
       <div className={css.container}>
         <div className={css.header}>
           <Search