Use time.zone functions instead of server time functions

(Time.zone.today vs Date.today)

spec/services/bill_signature_service_spec.rb

@@ -4,7 +4,7 @@ describe BillSignatureService do
   describe ".grouped_unsigned_operation_until" do
     subject { BillSignatureService.grouped_unsigned_operation_until(date).length }
 
-    let(:date) { Date.today }
+    let(:date) { Time.zone.today }
 
     context "when operations of several days need to be signed" do
       before do

spec/services/france_connect_service_spec.rb

@@ -33,7 +33,7 @@ describe FranceConnectService do
       expect(subject).to have_attributes({
         given_name: given_name,
         family_name: family_name,
-        birthdate: Date.parse(birthdate),
+        birthdate: Time.zone.parse(birthdate).to_date,
         birthplace: birthplace,
         gender: gender,
         email_france_connect: email,