crostini: Fix a string

We save the backup when upgrading to the My Files folder, not the
Downloads folder.

Bug: chromium:1064918
Test: None
Change-Id: I975771ef6e33e939b95bdeece223eeafa85c9af5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2307017
Commit-Queue: Fergus Dall <sidereal@google.com>
Reviewed-by: Fergus Dall <sidereal@google.com>
Auto-Submit: David Munro <davidmunro@google.com>
Cr-Commit-Position: refs/heads/master@{#790672}

chrome/app/chromeos_strings.grdp

@@ -4596,7 +4596,7 @@
     This window will close after cancellation is complete.
   </message>
   <message name="IDS_CROSTINI_UPGRADER_BACKUP_CHECKBOX_MESSAGE" desc="Text shown in the Crostini upgrader dialog next to the backup checkbox.">
-    Back up my apps and files to Downloads folder before upgrading Linux.
+    Back up my apps and files to My Files folder before upgrading Linux.
   </message>
   <message name="IDS_CROSTINI_UPGRADER_BACKUP_CHANGE_LOCATION" desc="Text shown in the Crostini upgrader dialog next to the backup checkbox with a link enabling the user to change the location to which files are backed up.">
     Change location

chrome/app/chromeos_strings_grdp/IDS_CROSTINI_UPGRADER_BACKUP_CHECKBOX_MESSAGE.png.sha1

+dd6b010a4e5a70c359f69b987a83d8420bef2597
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