Update generic Gitleak regex to remove false positives

[LewisArdern]

This update reduces FPs in the existing rule which was ported from gitleaks.

Due to the nature of this rule, its heavy false positive.

Initial rule:

Ran 1 rule on 75023 files: 582 findings.

39.07s user 8.19s system 142% cpu 33.202 total

Updated rule:

Ran 1 rule on 73139 files: 183 findings.

71.39s user 7.98s system 171% cpu 46.262 total