Update Chromium version number

Also make the number more general as we will be updating the patch
number at least once more before final.

Change-Id: Ie9bfffb8f87fdb2c08a416ca1b977f7b0afc8c32
Reviewed-by: Michael Brüning <michael.bruning@qt.io>

src/webengine/doc/src/qtwebengine-overview.qdoc

@@ -89,8 +89,8 @@
     \l{https://chromium.googlesource.com/chromium/src/+/master/docs/chromium_browser_vs_google_chrome.md}{overview}
     that is part of the documentation in the \l {Chromium Project} upstream source tree.
 
-    This version of Qt WebEngine is based on Chromium version 69.0.3497.128, with
-    additional security fixes from newer versions.
+    This version of Qt WebEngine is based on Chromium version 73.0.3683, with additional security
+    fixes from newer versions.
 
     \section2 Qt WebEngine Process