Upgrade to rust 1.69

[fuchsnj]

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[jszwedko]

I assume you've seen this, but #16212 was the start of the upgrade to 1.67.1 that got blocked in case you want to pull in any of those changes here.

[jszwedko]

Reopening since technically this issue hasn't been closed.

[fuchsnj]

Renaming to 1.69, since 1.68 gets an ICE with Vector. See #16745 (comment) for details.