Fix bc workflow.

[terabytesoftw]

Q	A
Is bugfix?	✔️
New feature?	❌
Breaks BC?	❌

[what-the-diff]

PR Summary

• Updated workflow name
  The workflow name was changed from "Roave BC Check" to "backwards compatibility".
• Removal of runs-on key
  The runs-on key is removed, and the job now uses a template instead.
• New os parameter added
  A new parameter called os was added with the value 'ubuntu-latest', enabling action execution on different operating systems (e.g., Windows).
• Introduction of php parameter
  A new parameter called php has been added, allowing for testing the code against multiple PHP versions simultaneously. Its default value is set to 8, considering current Yii package compatibility.