.python/SpellCheck: Increase SpellCheck plugin max failures

.python/SpellCheck: Increase SpellCheck plugin max failures

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=2593

Increases the maximum number of failures in the SpellCheck plugin so
that more issues can be caught in a single pass.

Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Sean Brogan <sean.brogan@microsoft.com>
Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>
Reviewed-by: Sean Brogan <sean.brogan@microsoft.com>
Reviewed-by: Shenglei Zhang <shenglei.zhang@intel.com>