Trigger page breaks if branch regex has invalid regex format

[dheeth]

Checklist:

• I've searched in the docs and FAQ for my answer
• I've included steps to reproduce the bug.

Describe the bug

If invalid regex is given in branch regex page, trigger page breaks after that

To Reproduce

1. Create a workflow with branch regex
2. Enter regex as "*" which is invalid
3. Save and try to trigger using build and deploy page

Expected behavior

It shouldn't break, either validate before save or show an error during trigger that regex is invalid

Current behavior

Trigger page gets broken when we try to trigger with invalid regex

AB#130