[FLINK-18660] Bump flink-shaded to 1.12; Bump netty to 4.1.49

[rmetzger]

Bump netty to 4.1.49 for some security fixes.
This also entails bumping netty-tcnative to 2.30.0

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[zentol]

+1 looks correct from what I see.

[rmetzger]

Thanks for your review. Merging.