PEP 817: add @rgommers to CODEOWNERS

Per #5171 (comment).

Signed-off-by: Michał Górny <mgorny@quansight.com>

Author: mgorny

.github/CODEOWNERS

@@ -693,8 +693,8 @@ peps/pep-0813.rst  @warsaw @ericvsmith
 peps/pep-0814.rst  @vstinner @corona10
 peps/pep-0815.rst  @emmatyping
 peps/pep-0816.rst  @brettcannon
-peps/pep-0817.rst  @warsaw @dstufft
-peps/pep-0817/     @warsaw @dstufft
+peps/pep-0817.rst  @warsaw @dstufft @rgommers
+peps/pep-0817/     @warsaw @dstufft @rgommers
 peps/pep-0818.rst  @hoodmane @ambv
 peps/pep-0819.rst  @emmatyping
 peps/pep-0820.rst  @encukou