UnitTestFrameworkPkg: CI YAML: Grant cmockery spell check exception

UnitTestFrameworkPkg: CI YAML: Grant cmockery spell check exception

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3798

UnitTestFrameworkPkg.dec contains cmockery folder from cmocka submodule.
However, the term "cmockery" is unrecognized by cspell tool.

This change grants spell check exception to "cmockery" to prevent
pipeline building failure.

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Sean Brogan <sean.brogan@microsoft.com>
Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>
Signed-off-by: Kun Qin <kuqin12@gmail.com>
Reviewed-by: Sean Brogan <sean.brogan@microsoft.com>