[Merged by Bors] - ci: Relax cache upload gating to upload cache artifacts from non-success builds

[marcelolynch]

Fixing an issue caught by @bryangingechen. We want to upload the build artifacts on failure also, so we run the cache job iff we had some artifacts to stage (and try to stage stuff whenever we had 'some' build)

[github-actions]

PR summary 3bbc5c706c

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 scripts/declarations_diff.sh contains some details about this script.

---

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).

[bryangingechen]

LGTM, but this will be easier to merge after #35389 goes in.

[bryangingechen]

#35389 is now on the queue, and there is a zulip thread about the issue this is fixing at #mathlib4 > New CI cache workflow not working properly @ 💬, so I will put this in the same batch.

Thanks!
bors r+

[mathlib-bors]

Pull request successfully merged into master.

Build succeeded:

• ci (staging) / Post-CI job
• ci (staging) / Post-Build Step
• ci (staging) / Lint style
• ci (staging) / Build