renovate: Improve PR creation reliability

[anomiex]

Proposed changes

Set pnpm's allowUnusedPatches to avoid erroring out for cases like #47472 (comment). Too bad pnpm 11 is removing ignorePatchFailures, that'd be useful for the PR creation too.

Also, try creating the change entries even if pnpm install fails, as the change entry creation doesn't depend on pnpm. The later tools/check-intra-monorepo-deps.sh run will fail, but getting change entries created is still an improvement.

Other information

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No

Testing instructions

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[tbradsha]

Looks like an improvement. Presumably allow-unused-patches would output some messaging even if unused patches exist? If not, and we miss it, I suppose it would result in errors on a local trunk and subsequent trunk-based branches.

[anomiex]

It'll result in failures in CI jobs on the Renovate PR itself after the PR is created. But the PR will be more complete, allowing it to be fixed with less work.