What does this PR do?

Fixes perma-failing update-snapshots gh action.

• Do not run nightly and instead allow manual runs
• Add missing $ARCH env var

Motivation

Testing Guidelines

Since there's currently no way to trigger this action manually, we won't be able to test until this is merged. I think that's fine, cuz we never use these jobs anyway.

Additional Notes

Types of Changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
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• This PR passes the integration tests (ask a Datadog member to run the tests)