ci: Fix a number of spellcheck issues

Includes the build directory in the spellcheck exclude list so the
checker can be run locally after a build has been done.
Fixes the include pattern for the meta-cassini-* directories so it
matches correctly.
Remove non-existent /gitlab directory from the exclude list.
Add used words to the dictionary to clear remaining existing issues.

Signed-off-by: Drew Reed <Drew.Reed@arm.com>