test: improve coverage of lib/os.js

PR-URL: #38653
Refs: https://coverage.nodejs.org/coverage-52e4fb5b23157222/lib/os.js.html#L96
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michael Dawson <midawson@redhat.com>

test/parallel/test-os.js

@@ -247,6 +247,7 @@ assert.strictEqual(`${os.endianness}`, os.endianness());
 assert.strictEqual(`${os.tmpdir}`, os.tmpdir());
 assert.strictEqual(`${os.arch}`, os.arch());
 assert.strictEqual(`${os.platform}`, os.platform());
+assert.strictEqual(`${os.version}`, os.version());
 
 assert.strictEqual(+os.totalmem, os.totalmem());