Add owners for test/ and test-run/

In order to improve tests of Tarantool core
assign dedicated team to perform review of each
and every change.

NO_CHANGELOG=no code changes
NO_TEST=no code changes
NO_DOC=no code changes

(cherry picked from commit 532bada7)

.github/CODEOWNERS

 # Documentation team is in charge of changelogs.
 # No changes should go w/o approval by doc team
 /changelogs/ @tarantool/doc
+/test/       @tarantool/devx
+/test-run/   @tarantool/devx