A ton of random bugs and polish (#3668)

Kavita.Common/Helpers/CronHelper.cs

@@ -13,7 +13,7 @@ public static class CronHelper
             CronExpression.Parse(cronExpression);
             return true;
         }
-        catch (Exception ex)
+        catch (Exception)
         {
             /* Swallow */
             return false;

Kavita.Common/Helpers/FlurlConfiguration.cs

@@ -28,7 +28,9 @@ public static class FlurlConfiguration
             if (ConfiguredClients.Contains(host)) return;
 
             FlurlHttp.ConfigureClientForUrl(url).ConfigureInnerHandler(cli =>
+#pragma warning disable S4830
                 cli.ServerCertificateCustomValidationCallback = (_, _, _, _) => true);
+#pragma warning restore S4830
 
             ConfiguredClients.Add(host);
         }