Remove redundant upgrade command in CI workflow

The `sudo apt-get -y upgrade` command was removed from the CI workflow's "Install sendmail" step. This change simplifies the installation process by ensuring only the necessary updates and installations are performed, which can contribute to faster and more reliable CI runs.

.github/workflows/ci.yml

@@ -50,7 +50,7 @@ jobs:
                   check-latest: true
             - name: Install sendmail
               run: |
-                sudo apt-get -y update && sudo apt-get -y upgrade && sudo DEBIAN_FRONTEND=noninteractive apt-get -y install nullmailer && which sendmail
+                sudo apt-get -y update && sudo DEBIAN_FRONTEND=noninteractive apt-get -y install nullmailer && which sendmail
             - name: Run go test
               if: success()
               run: |