chore: Pin all external actions to commit hash

[ppawlowski]

Description

This pull request pins all external GitHub Actions to their commit hash instead of tags.

Related Issue(s)

https://github.com/FlowFuse/CloudProject/issues/663

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
  • Upgrade instructions
  • Configuration details
  • Concepts
• Changes flowforge.yml?
  • Issue/PR raised on FlowFuse/helm to update ConfigMap Template
  • Issue/PR raised on FlowFuse/CloudProject to update values for Staging/Production

Labels

• Includes a DB migration? -> add the area:migration label

[hardillb]

@ppawlowski Did you mean to add the new file as well as update the versions?

.github/workflows/notify_on_slack.yml

[ppawlowski]

@ppawlowski Did you mean to add the new file as well as update the versions?

.github/workflows/notify_on_slack.yml

Nope, thank you!