Can't use env in config file

[fewensa]

Describe the bug
Can't not use env in slack.yml

To Reproduce

1. Add env to action https://github.com/darwinia-network/apps-lite/blob/915e6b2a0333e75a8f9e33cd6326c1ce1f7a772c/.github/workflows/deploy-dev.yml#L54
2. Read env from slack.yml https://github.com/darwinia-network/apps-lite/blob/915e6b2a0333e75a8f9e33cd6326c1ce1f7a772c/.github/config/slack-vercel.yml#L88
3. https://github.com/darwinia-network/apps-lite/runs/4824566165?check_suite_focus=true#step:9:10

Expected behavior
Can read this env from slack.yml

Screenshots

Additional context
I'm tested use default slack.yml it works, read from env happened this error.

[satterly]

Can you enable debug and run again? Thanks.

To enable runner diagnostic logging set the ACTIONS_RUNNER_DEBUG secret to true.
To enable step debug logging set the ACTIONS_STEP_DEBUG secret to true.

[satterly]

The env context is available in config file templates via {{env.VARIABLE_NAME}} — this uses process.env which includes all environment variables set at the workflow, job, or step level.

Common causes for env values showing as empty or undefined:

1. YAML quoting — Values containing {{ must be quoted in YAML config files:

   # Wrong — YAML may interpret {{ as a flow mapping
   text: Visit {{env.VERCEL_URL}}
   
   # Correct
   text: "Visit {{env.VERCEL_URL}}"

2. Variable not set — Ensure the env var is defined at the workflow, job, or step level before the slack action step runs.

Closing as stale since there was no follow-up after the debug request. Please reopen if you can reproduce with debug logging enabled.