fix: wrap h4 CSS selectors in :global() to silence unused-selector warnings

The h4 elements are injected by MDsveX markdown rendering at runtime,
not present in the static Svelte template, so Svelte's scoped CSS
analyser correctly cannot find them. Using :global() mirrors how the
existing blockquote rule in the same file is already handled.

Author: josecelano

src/routes/blog/deploying-torrust-tracker-with-the-deployer/+page.svelte

@@ -1598,7 +1598,7 @@ docker run --rm \\
 		color: rgba(245, 245, 245, 0.88);
 	}
 
-	h4 {
+	:global(h4) {
 		font-size: 1.25rem;
 		font-weight: bold;
 		padding-top: 1rem;
@@ -1679,7 +1679,7 @@ docker run --rm \\
 	.content-preview > ol,
 	.content-preview > h2,
 	.content-preview > h3,
-	.content-preview > h4 {
+	:global(.content-preview > h4) {
 		margin-bottom: 1rem;
 	}