[iOS] Disable testRepostFormAfterTappingBack.

This test is failing on iPad for the slim nav bot.

TBR=eugenebut@chromium.org
NOTRY=true

Bug: 968296
Change-Id: I231bf42f8c8fa3aa2f1bf3195e31f9b69a085543
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1639086
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Reviewed-by: Justin Cohen <justincohen@chromium.org>
Auto-Submit: Kurt Horimoto <kkhorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#665579}

ios/chrome/browser/web/forms_egtest.mm

@@ -242,6 +242,11 @@ id<GREYMatcher> ResendPostButtonMatcher() {
 // Tests that a POST followed by navigating to a new page and then tapping back
 // to the form result page resends data.
 - (void)testRepostFormAfterTappingBack {
+  // TODO(crbug.com/968296): Test is failing on iPad for slim nav.
+  if (IsIPadIdiom() && web::GetWebClient()->IsSlimNavigationManagerEnabled()) {
+    EARL_GREY_TEST_DISABLED(@"Test disabled on iPad.");
+  }
+
   [self setUpFormTestSimpleHttpServer];
   const GURL destinationURL = GetDestinationUrl();