I think to appease both systems we need to put the inner bulleted list
inside a block. I think that is OK in this case because there is no
inner block marker to worry about. So:

diff --git a/Documentation/config/extensions.adoc b/Documentation/config/extensions.adoc
index 49a7598ca5..aaea8c107f 100644
--- a/Documentation/config/extensions.adoc
+++ b/Documentation/config/extensions.adoc

@@ -55,8 +55,9 @@ For historical reasons, this extension is respected regardless of the
 refStorage:::
 	Specify the ref storage format to use. The acceptable values are:
 +
+--
 include::../ref-storage-format.adoc[]
-
+--
 +
 Note that this setting should only be set by linkgit:git-init[1] or
 linkgit:git-clone[1]. Trying to change it after initialization will not

on top of your patch seems to do the right thing (no change in asciidoc,
and eliminating the regression from your patch). It's a little gross
because we are reaching across the include to realize that
ref-storage-format.adoc contains a list that needs to go into its own
block. I wonder if asciidoc implicitly opens a new block for an include
but asciidoctor doesn't. But at any rate, this is the only way I could
come up with for both to render correctly.