Nominate Vlad Serebrennikov for C++ DRs

Vlad has been improving our C++ DR conformance testing story for many
months at this point and writing these kinds of test is sometimes non-
trivial, so having a maintainer specific for this is helpful.

Author: AaronBallman

clang/Maintainers.rst

@@ -226,6 +226,12 @@ C++ conformance
 | hubert.reinterpretcast\@gmail.com (email), hubert.reinterpretcast (Phabricator), hubert-reinterpretcast (GitHub)
 
 
+C++ Defect Reports
+~~~~~~~~~~~~~~~~~~
+| Vlad Serebrennikov
+| serebrennikov.vladislav\@gmail.com (email), Endilll (GitHub), Endill (Discord), Endill (Discourse)
+
+
 Objective-C/C++ conformance
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
 | John McCall