fix: reject ListMultipartUploads requests that also carry uploadId

A bucket GET with both the uploads and uploadId query parameters was
routed to ListMultipartUploads and answered with the upload listing.
S3 rejects the combination with 400 InvalidArgument, "Conflicting query
string parameters: uploadId, uploads".

Add an error route for the combination ahead of ListMultipartUploads,
the way the object level '?uploads' request is rejected, and enable
the REST test that covers it.

Fixes #2155

s3api/router.go

@@ -725,6 +725,11 @@ func (sa *S3ApiRouter) Init() {
 			middlewares.VerifyV4Signature(sa.root, sa.iam, sa.region, false, false, false),
 			middlewares.ParseAcl(sa.be),
 		))
+	// bucket operation with both '?uploads' and '?uploadId' is rejected
+	bucketRouter.Get("",
+		middlewares.MatchQueryArgs("uploads", "uploadId"),
+		controllers.ProcessHandlers(ctrl.HandleErrorRoute(s3err.GetInvalidArgumentErr(s3err.InvalidArgUploadIdWithUploads, "uploadId")), metrics.ActionUndetected, services),
+	)
 	bucketRouter.Get("",
 		middlewares.MatchQueryArgs("uploads"),
 		controllers.ProcessHandlers(