[skip ci] Add myself as CODEOWNER for a couple of extensions

Mainly because I'm the one who's touched them the most recently and has a vague idea how these extensions work.

Author: Girgias

CODEOWNERS

@@ -11,9 +11,14 @@
 *.stub.php @kocsismate
 /.github @iluuu1994 @TimWolla
 /build/gen_stub.php @kocsismate
+/ext/dba @Girgias
 /ext/ffi @dstogov
+/ext/gmp @Girgias
+/ext/imap @Girgias
 /ext/opcache @dstogov @iluuu1994
 /ext/random @TimWolla
+/ext/session @Girgias
+/ext/spl @Girgias
 /Zend @iluuu1994
 /Zend/Optimizer @dstogov
 /Zend/zend.* @dstogov