fix: Add required version field to test mcpp.toml

mcpp 0.0.81 (CI version) requires package.version field.
Successfully tested with mcpp 0.0.81:
- Build: ✓ Downloaded compat.tomlplusplus v3.4.0 from GitHub
- Compile: ✓ C++23 module + test binary (5.78s)
- Run: ✓ Output 'toml++ test: OK'

Author: yspbwx2010

tests/examples/tomlplusplus/mcpp.toml

@@ -1,5 +1,6 @@
 [package]
 name = "test-tomlplusplus"
+version = "0.1.0"
 
 [targets.test-tomlplusplus]
 kind = "bin"