Only target main frame navigations for link tracking (duckduckgo#2052)

Author: SlayterDev

DuckDuckGo/TabViewController.swift

@@ -1297,7 +1297,7 @@ extension TabViewController: WKNavigationDelegate {
 
         // This check needs to happen before GPC checks. Otherwise the navigation type may be rewritten to `.other`
         // which would skip link rewrites.
-        if navigationAction.navigationType != .backForward {
+        if navigationAction.navigationType != .backForward && navigationAction.isTargetingMainFrame() {
             let didRewriteLink = linkProtection.requestTrackingLinkRewrite(initiatingURL: webView.url,
                                                                            navigationAction: navigationAction,
                                                                            onStartExtracting: { showProgressIndicator() },