fix: disable forgotten password for external signin only (#6680)

- Make it such that `[service].ENABLE_INTERNAL_SIGNIN = false` disables the forgotten password prompt on the login page.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/6680
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: davrot <davrot@noreply.codeberg.org>
Co-committed-by: davrot <davrot@noreply.codeberg.org>

templates/user/auth/signin_inner.tmpl

@@ -50,6 +50,7 @@
 	</div>
 </div>
 
+{{if not .DisablePassword}}
 <div class="ui container fluid">
 	{{template "user/auth/webauthn_error" .}}
 
@@ -65,3 +66,5 @@
 			</div>
 		</div>
 </div>
+{{end}}
+