ci: remove special support for ProofWidgets4 cloud releases

[Vtec234]

This PR removes special support for ProofWidgets4 cloud releases. See leanprover-community/ProofWidgets4#165.

Branch on this repo to exercise the CI: https://github.com/leanprover-community/mathlib4/tree/rm-pw4-cache .

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[github-actions]

PR summary 34f85c5f24

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

- getProofWidgets

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).

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⚠️ Workflow documentation reminder

This PR modifies files under .github/workflows/.
Please update docs/workflows.md if the workflow inventory, triggers, or behavior changed.

Modified workflow files:

• .github/workflows/build_template.yml

[github-actions]

✅ PR Title Formatted Correctly

The title of this PR has been updated to match our commit style conventions.
Thank you!

[bryangingechen]

bors try

[Vtec234]

This was introduced in #31723. We no longer need to pin ProofWidgets4 to a specific tagged version after this PR. Indeed, all the other dependencies are required as main. But actually using a tagged version seems like good practice. So I see two options:

• Keep require proofwidgets at a tagged version, and keep this CI check.
• Use main, remove the CI check.

[Vtec234]

Hm, actually this seems to duplicate functionality of verify_proofwidgets_toolchain in scripts/verify_version_tags.py. But there are no references to that script (only meant to be run locally? introduced in #32162).

[Vtec234]

Superseded by #37290.