lib: Bump to ostree 0.19, cap-std-ext 3.0 && lib: Bump to rustix 0.38 && Bump semver to 0.12

[cgwalters]

keyfileext: Drop optional_string_list

Nothing is using this, and the underlying glib type changed so it's annoying to keep.

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lib: Bump to ostree 0.19, cap-std-ext 3.0

This is just "keeping up with churn":

• Newer versions of glib crates
• Bump to cap-std-ext 0.3, which bumps cap-std 2.0

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lib: Bump to rustix 0.38

Again just keeping up.

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lib: Bump semver to 0.12

Because we bumped ostree.

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