Slack action is limited to Linux only

[Borda]

🐛 Bug

The slack bot does not run on other OS:

Error: Container action is only supported on Linux

To Reproduce

https://github.com/PyTorchLightning/ecosystem-ci/runs/4601419524?check_suite_focus=true

Expected behavior

the Slack integration shall be running anywhere...

Additional context

See alternatives:

• https://github.com/marketplace/actions/slack-send
• https://github.com/act10ns/slack

[Borda]

resolved by #85