Fix alert management fingerprints

ActionController::Parameters class is prefixed with `#`.
The fingerprint in this case is totally different.

Let's rely on the .to_json output instead of .to_s
Its format is unlikely to change

ee/lib/gitlab/alert_management/payload/cilium.rb

@@ -18,7 +18,7 @@ module Gitlab
           fpayload = fpayload['flow'].except('time', 'Summary')
           fpayload['l4']['TCP'].delete('flags') if fpayload.dig('l4', 'TCP', 'flags')
 
-          fpayload.to_s
+          fpayload.to_json
         end
       end
     end

ee/spec/lib/gitlab/alert_management/payload/cilium_spec.rb

@@ -13,7 +13,7 @@ RSpec.describe Gitlab::AlertManagement::Payload::Cilium do
   it 'parses cilium specific fields' do
     expect(parsed_payload.title).to eq('Cilium Alert')
     expect(parsed_payload.description).to eq('POLICY_DENIED')
-    expect(parsed_payload.gitlab_fingerprint).to eq('b2ad2a791756abe01692270c6a846129a09891b3')
+    expect(parsed_payload.gitlab_fingerprint).to eq('23907c66f431ae66aad738553ccbd03e26f6838f')
   end
 
   context 'when title is not provided' do

ee/spec/services/alert_management/network_alert_service_spec.rb

@@ -31,7 +31,7 @@ RSpec.describe AlertManagement::NetworkAlertService do
           ended_at: nil,
           environment_id: nil,
           events:  1,
-          fingerprint: '89269ffa3902af37f036a77bc9ea57cdee3a52c2',
+          fingerprint: '23907c66f431ae66aad738553ccbd03e26f6838f',
           hosts: [],
           issue_id: nil,
           monitoring_tool: 'Cilium',
@@ -62,7 +62,7 @@ RSpec.describe AlertManagement::NetworkAlertService do
       it_behaves_like 'never-before-seen network alert'
 
       context 'for an existing alert with the same fingerprint' do
-        let_it_be(:fingerprint_sha) { '89269ffa3902af37f036a77bc9ea57cdee3a52c2' }
+        let_it_be(:fingerprint_sha) { '23907c66f431ae66aad738553ccbd03e26f6838f' }
 
         context 'which is triggered' do
           let_it_be(:alert) do