Add Fotis and Thomas Spriggs to the codeowners for /src/cbmc/

This folder contains files that manage the interface of the `cbmc` binary
(CLI option parsing, language init, etc).

Adding two long time CBMC contributors there should allow the
team to help contribute in reducing the review backlog for already
existing contributors, now and in the future, and also contribute in
maintaining a high code quality standard for that module going forward.

Author: NlightNFotis

CODEOWNERS

@@ -30,7 +30,7 @@
 
 # These files change frequently and changes are high-risk
 
-/src/cbmc/ @kroening @tautschnig @peterschrammel
+/src/cbmc/ @kroening @tautschnig @peterschrammel @NlightNFotis @thomasspriggs
 /src/goto-programs/ @kroening @tautschnig @peterschrammel
 /src/util/ @kroening @tautschnig @peterschrammel
 /src/solvers/refinement @martin-cs @romainbrenguier @peterschrammel