Added log to show which URL is blocked by CORS. (#26347)

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Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/api4/websocket_test.go

@@ -465,5 +465,5 @@ func TestWebSocketUpgrade(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, resp.StatusCode, http.StatusBadRequest)
 	require.NoError(t, th.TestLogger.Flush())
-	testlib.AssertLog(t, buffer, mlog.LvlDebug.Name, "Failed to upgrade websocket connection.")
+	testlib.AssertLog(t, buffer, mlog.LvlDebug.Name, "URL Blocked because of CORS. Url: ")
 }