[master] Fixes version parsing for WARNING situations

[Karm]

fixes graalvm/mandrel#766
fixes #429

From my test run 24.1 branch aarch64:

...
DEBUG [OperatingSystem] Execute [/home/tester/karm/mx/mx, graalvm-version] in /home/tester/karm/graal/substratevm with environment variables [MX_PYTHON=python]
INFO [build] mx's graalvm-version output: WARNING: No platform-specific definition is available for distribution MUSL_CMAKE_TOOLCHAIN for your architecture (aarch64)
INFO [build] mx's graalvm-version output: 24.1.0-dev
...
[1/8] Initializing...                                                                                    (3.7s @ 0.16GB)
 Java version: 23-beta+36-ea, vendor version: Mandrel-24.1.0-devc014e6a1067
 Graal compiler: optimization level: 2, target machine: compatibility
 C compiler: gcc (redhat, aarch64, 11.4.1)
...
INFO [build] Congratulations you successfully built Mandrel 24.1.0-devc014e6a1067 based on Java 23-beta+36-ea
...

Note the WARNING is logged as INFO, so it should be always visible.