Disable run user change in installation page (#22499)

The run user should not be changed on the installation page because it
will not be any effect to Gitea.

This PR disabled the input box of run user.

options/locale/locale_en-US.ini

@@ -224,7 +224,7 @@ repo_path_helper = Remote Git repositories will be saved to this directory.
 lfs_path = Git LFS Root Path
 lfs_path_helper = Files tracked by Git LFS will be stored in this directory. Leave empty to disable.
 run_user = Run As Username
-run_user_helper = Enter the operating system username that Gitea runs as. Note that this user must have access to the repository root path.
+run_user_helper = The operating system username that Gitea runs as. Note that this user must have access to the repository root path.
 domain = Server Domain
 domain_helper = Domain or host address for the server.
 ssh_port = SSH Server Port

templates/install.tmpl

@@ -119,7 +119,7 @@
 					</div>
 					<div class="inline required field {{if .Err_RunUser}}error{{end}}">
 						<label for="run_user">{{.locale.Tr "install.run_user"}}</label>
-						<input id="run_user" name="run_user" value="{{.run_user}}" required>
+						<input id="run_user" name="run_user" value="{{.run_user}}" readonly>
 						<span class="help">{{.locale.Tr "install.run_user_helper"}}</span>
 					</div>
 					<div class="inline required field">