scripts: dts: update pyyaml version

The currently used PyYaml version has some vulnerabilies as
described on the pull request description. It updates to
version 6.0, removing these supply chain vulnerabily.
The OSSF Scorecard was the tool used for discovering
 these vulnerabilties.

Signed-off-by: Javan lacerda <javanlacerda@google.com>
3 files changed