[GITEA] Maintain aspect ratio for auth icons

- When specifying an icon URL for a authentication source, it's forced
to be an width and height of 20px. However this didn't take into account
that icons could have an different aspect ratio of 1:1.
- This patch fixes that by instead using `max-width` and `max-height`
which will respect other aspect ratios.
- Resolves https://codeberg.org/forgejo/forgejo/issues/1234

(cherry picked from commit 3482739637)

services/auth/source/oauth2/providers.go

@@ -56,7 +56,7 @@ func (p *AuthSourceProvider) DisplayName() string {
 
 func (p *AuthSourceProvider) IconHTML() template.HTML {
 	if p.iconURL != "" {
-		img := fmt.Sprintf(`<img class="gt-mr-3" width="20" height="20" src="%s" alt="%s">`,
+		img := fmt.Sprintf(`<img class="gt-mr-3 oauth-provider-icon" src="%s" alt="%s">`,
 			html.EscapeString(p.iconURL), html.EscapeString(p.DisplayName()),
 		)
 		return template.HTML(img)

web_src/css/base.css

@@ -2289,3 +2289,8 @@ table th[data-sortt-desc] .svg {
   flex-wrap: wrap;
   gap: .25rem;
 }
+
+.oauth-provider-icon {
+  max-height: 20px;
+  max-width: 20px;
+}