Add codeowners for incremental SMT2

So that the team currently implementing this piece of work can approve
PRs on it.

Author: thomasspriggs

CODEOWNERS

@@ -54,6 +54,7 @@
 /jbmc/src/jdiff/ @smowton @peterschrammel
 /src/cpp/ @kroening @tautschnig @peterschrammel
 /src/solvers/smt2 @kroening @martin-cs @tautschnig @peterschrammel @allredj @romainbrenguier
+/src/solvers/smt2_incremental @peterschrammel @thomasspriggs @NlightNFotis @TGWDB @chrisr-diffblue
 /src/statement-list/ @kroening @tautschnig @peterschrammel @pkesseli
 
 /cmake/        @diffblue/diffblue-opensource