Fix case-sensitive AD self-add group comparison

[srkyn]

Summary

Fixes the Windows AD add Self to Group analytic so the self-add comparison is case-insensitive:

| where lower(user)=lower(src_user)

Why

Issue #4105 reports that matching can fail when the same account appears with different casing, for example user=DA-1 and src_user=da-1.

Validation

python scripts/validate_yaml.py detections/endpoint/windows_ad_add_self_to_group.yml

Result:

[PASS] All 1 file(s) passed validation!

Fixes #4105.

[srkyn]

Rechecked this branch after the failed CI run. The PR diff is still limited to the intended case-insensitive comparison plus version/date bump, and the detection YAML parses cleanly.

Local sanity check passed:

• confirmed lower(user)=lower(src_user) is present
• confirmed version is bumped to 11
• parsed detections/endpoint/windows_ad_add_self_to_group.yml with PyYAML

The two failing GitHub Actions jobs appear to be blocked before exercising this detection because forked PR runs do not receive Splunk credentials:

• appinspect: APPINSPECTUSERNAME / APPINSPECTPASSWORD are empty, then Splunk API login returns 400 Client Error
• unit-testing: contentctl-ng install exits with Splunkbase credentials not provided in environment variables

The other checks (YAML Validation, build, and response template build) passed.

[patel-bhavin]

@srkyn - thank you for the PR and doing the testing locally, I think the fix makes sense and I will raise this issue of unit-testing needing creds. We recently updated our tooling and didnt think of this issue coming up! I will get back to you!