Fix flaky test in overdue patient specs (#5383)

**Story card:**
[sc-10942](https://app.shortcut.com/simpledotorg/story/10942/investigate-flaky-test-in-overdue-patients-in-region-summary-spec)

## Because

The test for `return the count of contactable patients returned to care
who were removed from overdue list` is flaky.
 
Current test arrangement:
- [One of the
patients](https://github.com/simpledotorg/simple-server/blob/0e548dcafba79c72357a5367b3182496725c4ff0/spec/models/reports/region_summary_spec.rb#L1469)
has 2 call results, one in the previous month and one in the current
month.
 - The patient returns to care on `the 2nd of the current month`.  
- The test will pass if the visit date of the patient fall within 15
days of the call .i.e (visit date - call date <=15).
 - First call was made on `1.month.ago`. 
- `1.month.ago` is relative to the current day and the date changes
daily.
 
For eg, assume today is 31-Jan-2024
 - date of first call: `1.month.ago` = 31-Dec-2023 (changes daily)
 - visit date: `one_month_ago + 2.days` = 2-Jan-2023 (fixed date)
- The test pass only when `(visit date - date of first call) <= 15`.
Since this difference (visit date - date of first call) changes daily,
the test turned to be flaky.

## This addresses

- Use a fixed date for `date of first call`
- date of first call: `one_month_ago + 20.days` = 20-Dec-2023 (A random
date which falls in the 15 day window)
- [`one_month_ago +
20.days`](https://github.com/simpledotorg/simple-server/blob/0e548dcafba79c72357a5367b3182496725c4ff0/spec/models/reports/region_summary_spec.rb#L734)
is always the 20th of the previous month.

spec/factories/patients.rb

@@ -142,10 +142,14 @@
     trait(:removed_from_overdue_list) do
       transient do
         user { create(:user, registration_facility: registration_facility) }
+        call_date { 1.month.ago }
       end
       recorded_at { 2.years.ago }
       with_overdue_appointments
-      call_results { build_list(:call_result, 1, user_id: user.id, appointment_id: appointments.first.id, result_type: :removed_from_overdue_list, remove_reason: CallResult.remove_reasons.keys.sample, device_created_at: 1.month.ago) }
+      call_results {
+        build_list(:call_result, 1, user_id: user.id, appointment_id: appointments.first.id, result_type: :removed_from_overdue_list,
+                                                 remove_reason: CallResult.remove_reasons.keys.sample, device_created_at: call_date)
+      }
     end
   end
 end

spec/models/reports/region_summary_spec.rb

@@ -1461,12 +1461,12 @@
       end
     end
 
-    xit "return the count of contactable patients returned to care who were removed from overdue list" do
+    it "return the count of contactable patients returned to care who were removed from overdue list" do
       facility_1_contactable_patients = create_list(:patient, 3, :with_sanitized_phone_number, :hypertension, assigned_facility: facility_1, recorded_at: five_months_ago)
       facility_1_contactable_patients.each { |patient| create(:appointment, patient: patient, device_created_at: three_months_ago, scheduled_date: three_months_ago + 14.days) }
       facility_1_patients_without_phone = create(:patient, :without_phone_number, :hypertension, assigned_facility: facility_1, recorded_at: five_months_ago)
       create(:appointment, patient: facility_1_patients_without_phone, device_created_at: three_months_ago, scheduled_date: three_months_ago + 14.days)
-      facility_1_patients_removed_from_list = create(:patient, :removed_from_overdue_list, :hypertension, assigned_facility: facility_1, recorded_at: five_months_ago)
+      facility_1_patients_removed_from_list = create(:patient, :hypertension, :removed_from_overdue_list, call_date: one_month_ago + 20.days, assigned_facility: facility_1, recorded_at: five_months_ago)
       create(:appointment, patient: facility_1_patients_removed_from_list, device_created_at: three_months_ago, scheduled_date: three_months_ago + 14.days)
 
       create(:call_result, patient: facility_1_patients_without_phone, result_type: "removed_from_overdue_list", remove_reason: "other", device_created_at: this_month)