s/urf-8/utf-8 on manual config profile download (#23169)

# Checklist for submitter

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<!-- Note that API documentation changes are now addressed by the
product design team. -->

- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
See [Changes
files](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/Committing-Changes.md#changes-files)
for more information.
- [x] Manual QA for all new/changed functionality

changes/urf-8

@@ -0,0 +1 @@
+* Fixed incorrect character set header on manual Mac enrollment config download

docs/REST API/rest-api.md

@@ -5867,7 +5867,7 @@ Learn more about OTA profiles [here](https://developer.apple.com/library/archive
 
 ```http
   Content-Length: 542
-  Content-Type: application/x-apple-aspen-config; charset=urf-8
+  Content-Type: application/x-apple-aspen-config; charset=utf-8
   Content-Disposition: attachment;filename="fleet-mdm-enrollment-profile.mobileconfig"
   X-Content-Type-Options: nosniff
 ```

server/service/devices.go

@@ -498,7 +498,7 @@ func (r getDeviceMDMManualEnrollProfileResponse) hijackRender(ctx context.Contex
 	// detect short writes (if it fails to send the full content properly)
 	w.Header().Set("Content-Length", strconv.FormatInt(int64(len(r.Profile)), 10))
 	// this content type will make macos open the profile with the proper application
-	w.Header().Set("Content-Type", "application/x-apple-aspen-config; charset=urf-8")
+	w.Header().Set("Content-Type", "application/x-apple-aspen-config; charset=utf-8")
 	// prevent detection of content, obey the provided content-type
 	w.Header().Set("X-Content-Type-Options", "nosniff")