Fix broken time sync leeway with Geo

Previous versions did not properly set the IAT leeway properly, causing
many Geo API requests to be marked invalid. The problem was that
the ruby-jwt `master` used `iat_leeway` as the parameter, but v1.5.6
actually used `leeway`.

changelogs/unreleased-ee/sh-geo-fix-iat.yml

+---
+title: Fix broken time sync leeway with Geo
+merge_request:
+author:

lib/gitlab/geo/jwt_request_decoder.rb

@@ -41,7 +41,7 @@ module Gitlab
             encoded_message,
             secret,
             true,
-            { iat_leeway: IAT_LEEWAY, verify_iat: true, algorithm: 'HS256' }
+            { leeway: IAT_LEEWAY, verify_iat: true, algorithm: 'HS256' }
           )
 
           message = decoded.first

spec/lib/gitlab/geo/jwt_request_decoder_spec.rb

@@ -27,10 +27,16 @@ describe Gitlab::Geo::JwtRequestDecoder do
       expect(described_class.new(data).decode).to be_nil
     end
 
+    it 'successfully decodes when clocks are off by IAT leeway' do
+      subject
+
+      Timecop.travel(30.seconds.ago) { expect(subject.decode).to eq(data) }
+    end
+
     it 'returns nil when clocks are not in sync' do
-      allow(JWT).to receive(:decode).and_raise(JWT::InvalidIatError)
+      subject
 
-      expect(subject.decode).to be_nil
+      Timecop.travel(2.minutes.ago) { expect(subject.decode).to be_nil }
     end
 
     it 'raises invalid decryption key error' do