bitbake: SignatureGenerator: Add empty implementation for dump_sigs

* bitbake -S throws exception when 'noop' signature handler is used

[YOCTO #5738]

(Bitbake rev: 53352e8d388b7fc4da73f95b93dcc087e76d0426)

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/siggen.py

@@ -57,6 +57,8 @@ class SignatureGenerator(object):
     def invalidate_task(self, task, d, fn):
         bb.build.del_stamp(task, d, fn)
 
+    def dump_sigs(self, dataCache):
+        return
 
 class SignatureGeneratorBasic(SignatureGenerator):
     """