install swagger from source

First of all this removes the need for a network connection, second
renovate can update the version as it is tracked in go.mod.

However the real important part is that the binary downloads are
broken[1]. For some reason the swagger created with them does not
include all the type information for the examples. However when building
from source the same thing works fine.

[1] https://github.com/go-swagger/go-swagger/issues/2842

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

test/tools/vendor/github.com/go-openapi/runtime/discard.go

@@ -0,0 +1,9 @@
+package runtime
+
+import "io"
+
+// DiscardConsumer does absolutely nothing, it's a black hole.
+var DiscardConsumer = ConsumerFunc(func(_ io.Reader, _ interface{}) error { return nil })
+
+// DiscardProducer does absolutely nothing, it's a black hole.
+var DiscardProducer = ProducerFunc(func(_ io.Writer, _ interface{}) error { return nil })