Fix IsObjectExist with gogit (#31790)

Fix #31271.

When gogit is enabled, `IsObjectExist` calls
`repo.gogitRepo.ResolveRevision`, which is not correct. It's for
checking references not objects, it could work with commit hash since
it's both a valid reference and a commit object, but it doesn't work
with blob objects.

So it causes #31271 because it reports that all blob objects do not
exist.

modules/markup/html.go

@@ -1144,7 +1144,8 @@ func hashCurrentPatternProcessor(ctx *RenderContext, node *html.Node) {
 				})
 			}
 
-			exist = ctx.GitRepo.IsObjectExist(hash)
+			// Don't use IsObjectExist since it doesn't support short hashs with gogit edition.
+			exist = ctx.GitRepo.IsReferenceExist(hash)
 			ctx.ShaExistCache[hash] = exist
 		}