feat(scripts/autolabel): allow up to 3 topic labels to be added

[joneugster]

Quick, small improvement to the autolabelling script to allow up to three labels to be added.

This could be further refined to exclude labels of "lower level areas" (e.g. only t-algebraic-geometry instead of [t-algebraic-geometry, t-algebraic, t-data]) or to infer the label from the PR title (e.g. feat(Algebra/...): ...), but this might be a bigger refactor which does not fit into my available time.

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Zulip discussion: #mathlib reviewers > Proposal: automatic reviewer assignment @ 💬

[github-actions]

PR summary ca7d6f198f

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/declarations_diff.sh <optional_commit>

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

The doc-module for script/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/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).