chore: bump toolchain to v4.30.0-rc2

[Garmelon]

No description provided.

[github-actions]

PR summary 96c2df6e3d

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

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Declarations diff

No declarations were harmed in the making of this PR! 🐙

You can run this locally as follows

## summary with just the declaration names:
./scripts/pr_summary/declarations_diff.sh <optional_commit>

## more verbose report:
./scripts/pr_summary/declarations_diff.sh long <optional_commit>

The doc-module for scripts/pr_summary/declarations_diff.sh contains some details about this script.

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No changes to technical debt.

You can run this locally as

./scripts/reporting/technical-debt-metrics.sh pr_summary

• The relative value is the weighted sum of the differences with weight given by the inverse of the current value of the statistic.
• The absolute value is the relative value divided by the total sum of the inverses of the current values (i.e. the weighted average of the differences).

[Garmelon]

I'm unsure what to do about the minImports linter tests. Should the tests just accept the changed behavior or should the linter ignore Init.*?

leanprover/lean4#13323 is part of rc2 and may be related?
leanprover-community/import-graph#116 may also be related.