Avoid losing token when updating mirror settings (#30429) (#30464)

Backport #30429 by @wolfogre

Fix #30416.

Before (it shows as "Unset" while there's a token):

<img width="980" alt="image"
src="d7148e3e-62c9-4d2e-942d-3d795b79515a">

After:

<img width="977" alt="image"
src="24aaa1db-5baa-4204-9081-470b15ea72b5">

The username shows as "oauth2" because of
f9fdac9809/services/migrations/dump.go (L99)

I have checked that all usage of `MirrorRemoteAddress` has been updated.

<img width="1806" alt="image"
src="2f042501-2824-4511-9203-c84a6731a02d">

However, it needs to be checked again when backporting.

Co-authored-by: Jason Song <i@wolfogre.com>
(cherry picked from commit 92f4cd9461949940427f789a345a3a51b2de02bf)

templates/repo/settings/options.tmpl

@@ -156,7 +156,7 @@
 											<label for="interval">{{ctx.Locale.Tr "repo.mirror_interval" .MinimumMirrorInterval}}</label>
 											<input id="interval" name="interval" value="{{.PullMirror.Interval}}">
 										</div>
-										{{$address := MirrorRemoteAddress $.Context .Repository .PullMirror.GetRemoteName false}}
+										{{$address := MirrorRemoteAddress $.Context .Repository .PullMirror.GetRemoteName}}
 										<div class="field {{if .Err_MirrorAddress}}error{{end}}">
 											<label for="mirror_address">{{ctx.Locale.Tr "repo.mirror_address"}}</label>
 											<input id="mirror_address" name="mirror_address" value="{{$address.Address}}" required>