Field pattern not working correctly on creating/editing posts

**Describe the bug**
We have some fields with pattern usage like `/^.{0,130}$/gmi`
If I create a new post, this works fine.
But when I edit a post, I receive an error message, that the fields content doesn't match my regex pattern.
Sometimes it works and sometimes it won't, seems to be very flaky ....

Works correctly

Should also work correctly

**To Reproduce**
1. Create a field configuration with a field like
`{
label: 'Teaser',
name: 'teaser',
widget: 'text',
pattern: [/^.{0,130}$/gmi, 'Max amount of 130 characters'],
}`

2. Create a new post with this field filled correctly (tested this using regexr.com)
3. Save the new post, all should works fine
4. Edit the post and add or remove a line
5. Try to save it, you'll receive an error

**Expected behavior**
Pattern work correctly on editing

**Screenshots**
See above

**Applicable Versions:**
- "netlify-cms-app": "^2.15.72",