Add IHS Medicaid work requirement exclusion

Author: daphnehanse11

policyengine_us/tests/policy/baseline/gov/hhs/medicaid/eligibility/medicaid_work_requirement_eligible.yaml

@@ -127,3 +127,11 @@
     is_incarcerated: true
   output:
     medicaid_work_requirement_eligible: true
+
+- name: Case 15, person with Indian Health Service coverage is excluded from the work requirement.
+  period: 2027
+  input:
+    age: 30
+    has_indian_health_service_coverage_at_interview: true
+  output:
+    medicaid_work_requirement_eligible: true

policyengine_us/variables/gov/hhs/medicaid/eligibility/medicaid_work_requirement_eligible.py

@@ -37,6 +37,10 @@ def formula(person, period, parameters):
         former_foster_care_youth = was_in_foster_care & (
             age < p.former_foster_care_age_limit
         )
+        # American Indian or Alaska Native / IHS eligibility exclusion.
+        has_ihs_coverage = person(
+            "has_indian_health_service_coverage_at_interview", period
+        )
         # Entitled to or enrolled in Medicare Part A or B.
         medicare_eligible = person("is_medicare_eligible", period)
         # parent, guardian, caretaker of a disabled person
@@ -63,6 +67,7 @@ def formula(person, period, parameters):
             is_enrolled_at_least_half_time
             | is_pregnant_or_postpartum
             | former_foster_care_youth
+            | has_ihs_coverage
             | medicare_eligible
             | has_disabled
             | eligible_veteran