@W-24276452: read inputs from envs

[iowillhoit]

What does this PR do?

Updates .github/workflows/publish-providers.yml to read a few values from environment variables instead of interpolating them directly into run: scripts.

Values now passed via env::

• github.event_name → EVENT_NAME
• inputs.packages → PACKAGES_INPUT
• matrix.package → MATRIX_PACKAGE
• steps.changelog.outputs.version → PUBLISHED_VERSION

No behavior change for normal usage.

What issues does this PR fix or reference?

@W-24276452@

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