Fix runner button height (#24338)

Fixes https://github.com/go-gitea/gitea/issues/24326.

Set size class and downsize any such buttons that have a dropdown icon
because the dropdown icon increases button height artificially.

[`:has()`](https://developer.mozilla.org/en-US/docs/Web/CSS/:has) is not
supported in Firefox yet, but works fine with the experimental pref
enabled. I see this as a graceful degradation in unsupporting browsers.

templates/shared/actions/runner_list.tmpl

@@ -4,7 +4,7 @@
 		{{.locale.Tr "actions.runners.runner_manage_panel"}} ({{.locale.Tr "admin.total" .Total}})
 		<div class="ui right">
 			<div class="ui top right pointing dropdown">
-				<button class="ui button primary">
+				<button class="ui primary tiny button">
 					{{.locale.Tr "actions.runners.new"}}
 					{{svg "octicon-triangle-down" 14 "dropdown icon"}}
 				</button>