test: parse WSL kernel version without error

[papparapa]

The WSL kernel version is not SemVer compliant, e.g. 6.6.87.1-microsoft-standard-WSL2, which causes a version check error during the io_uring test on WSL.

error: 'os.linux.IoUring.test.openat_direct/close_direct' failed: /workspaces/Zig/zig/lib/std/SemanticVersion.zig:95:28: 0x107c3e9 in parse (test)
    if (it.next() != null) return error.InvalidVersion;
                           ^
/workspaces/Zig/zig/lib/std/os/linux/IoUring.zig:3978:5: 0x21f2dd1 in test.openat_direct/close_direct (test)
    try skipKernelLessThan(.{ .major = 5, .minor = 19, .patch = 0 });
    ^

This PR modifies the version check function to extract the SemVer-compliant part of the WSL kernel version, as in #20001.