Adds git commit author + message to deployment notification with this ArgoCD patch

patch-argo-notif-cm.yaml

---
apiVersion: v1
kind: ConfigMap
metadata:
  name: argocd-notifications-cm
  namespace: argocd
data:
  template.app-deployed: |
    email:
      subject: New version of an application {{.app.metadata.name}} is up and running.
    message: |
      {{if eq .serviceType "slack"}}:white_check_mark:{{end}} Application {{.app.metadata.name}} is now running new version of deployments manifests.
    slack:
      attachments: |
        [{
          "title": "{{ .app.metadata.name}}",
          "title_link":"{{.context.argocdUrl}}/applications/{{.app.metadata.name}}",
          "color": "#18be52",
          "fields": [
          {
            "title": "Sync Status",
            "value": "{{.app.status.sync.status}}",
            "short": true
          },
          {
            "title": "Repository",
            "value": "{{.app.spec.source.repoURL}}",
            "short": true
          },
          {
            "title": "Revision",
            "value": "{{.app.status.sync.revision}}",
            "short": true
          },
          {{- $commitMeta := (call .repo.GetCommitMetadata .app.status.sync.revision) }}
          {
            "title": "Author",
            "value": "{{ ($commitMeta).Author }}",
            "short": true
          },
          {
            "title": "Message",
            "value": "{{ (call .strings.ReplaceAll ($commitMeta).Message "\n" "\\n") }}",
            "short": true
          }
          {{range $index, $c := .app.status.conditions}}
          {{if not $index}},{{end}}
          {{if $index}},{{end}}
          {
            "title": "{{$c.type}}",
            "value": "{{$c.message}}",
            "short": true
          }
          {{end}}
          ]
        }]
      groupingKey: ""
      notifyBroadcast: false
    teams:
      facts: |
        [{
          "name": "Sync Status",
          "value": "{{.app.status.sync.status}}"
        },
        {
          "name": "Repository",
          "value": "{{.app.spec.source.repoURL}}"
        },
        {
          "name": "Revision",
          "value": "{{.app.status.sync.revision}}"
        }
        {{range $index, $c := .app.status.conditions}}
          {{if not $index}},{{end}}
          {{if $index}},{{end}}
          {
            "name": "{{$c.type}}",
            "value": "{{$c.message}}"
          }
        {{end}}
        ]
      potentialAction: |-
        [{
          "@type":"OpenUri",
          "name":"Operation Application",
          "targets":[{
            "os":"default",
            "uri":"{{.context.argocdUrl}}/applications/{{.app.metadata.name}}"
          }]
        },
        {
          "@type":"OpenUri",
          "name":"Open Repository",
          "targets":[{
            "os":"default",
            "uri":"{{.app.spec.source.repoURL | call .repo.RepoURLToHTTPS}}"
          }]
        }]
      themeColor: "#000080"
      title: New version of an application {{.app.metadata.name}} is up and running.

Multi-line message handled with:
argoproj/argo-cd#9069 (comment)