We have ~2.5k nodes running Void Linux, which report a version string
like `1.96.2_1 (Void Linux)`. Previously these versions would fail to
parse, because we only expect a hyphen and `extraCommits` after the
major/minor/patch numbers.
Fix the version parsing logic to handle this case.
Updates #19148
Change-Id: Ica4f172d080af266af7f0d69bb31483a095cd199
Signed-off-by: Alex Chan <alexc@tailscale.com>