Bump msgpack to +borg2 after build fix backports

src/borg/algorithms/msgpack/_version.py

@@ -2,5 +2,9 @@
 # Changes:
 # +borg1: drop support for old buffer protocol to be compatible with py310
 #         (backport of commit 9ae43709e42092c7f6a4e990d696d9005fa1623d)
-version = (0, 5, 6, '+borg1')
+# +borg2: Usef __BYTE_ORDER__ instead of __BYTE_ORDER (#513)
+#         (backport of commit 9d45926a596028e39ec59dd909a56eb5e9e8fee7)
+#         Fix build error caused by ntohs, ntohl (#514)
+#         (backport of commit edca770071fc702e0b4c33f87fb0fa3682b486b4)
+version = (0, 5, 6, '+borg2')