Bump the version this package calls itself, which the repin forgot

The previous commit is titled 0.4.0, moves the openkal requirement to 0.10.0,
and left `version' at 0.3.0. openkal-musl 0.11.0 requires openkal-opensbi
0.4.0, so releasing this as-is would tag a 0.4.0 whose manifest says 0.3.0 and
leave that requirement pointing at a package that does not answer to the name.

Found by checking every self-version in the chain against what its consumers
require. It is the only one that disagreed.

Author: Sunrisepeak

mcpp.toml

@@ -14,7 +14,7 @@
 [package]
 namespace   = "mcpplibs"
 name        = "openkal-opensbi"
-version     = "0.3.0"
+version     = "0.4.0"
 description = "An implementation of openkal on the RISC-V Supervisor Binary Interface, portable across every machine whose firmware provides one"
 license     = "Apache-2.0"