imgtool: fix signing for fix-sig-pubkey public rsa

Add keys.RSAPublic to allowed key SHA dictionary.

Signed-off-by: Georgij Cernysiov <geo.cgv@gmail.com>

Author: GeorgeCGV

scripts/imgtool/image.py

@@ -184,6 +184,7 @@ def tlv_sha_to_sha(tlv):
     keys.ECDSA384P1Public   : ['384'],
     keys.ECDSA256P1         : ['256'],
     keys.RSA                : ['256'],
+    keys.RSAPublic          : ['256'],
     # This two are set to 256 for compatibility, the right would be 512
     keys.Ed25519            : ['256', '512'],
     keys.X25519             : ['256', '512']