[BUG] RegExp are proxified which breaks them

[CGNonofr]

Describe the bug
Due to this commit, regexes are now broken.

If your configuration contains a regex, you'll get a proxified regex which seems to be ok but it will crash as soon as you try to use it with an error: TypeError: RegExp.prototype.source getter called on non-RegExp object

Expected behavior
You can put regexes in your config files (in cjs or ts format) and use it in your code

Please tell us about your environment:

• node-config version: 3.3.9
• node-version: 16.19.1

Other information

A workaround is to enable ALLOW_CONFIG_MUTATIONS but it's not an acceptable solution