Add Docker login back for pushing from main

[johscheuer]

Description

In #1355 we did some refactoring and missed to add the login step if we operator on the main branch.

Type of change

Please select one of the options below.

• Bug fix (non-breaking change which fixes an issue)

Discussion

Testing

Documentation

Follow-up

[foundationdb-ci]

Result of fdb-kubernetes-operator-pr on Linux CentOS 7

• Commit ID: 2bdfdb1
• Duration 4:06:08
• Result: ❌ FAILED
• Error: Error while executing command: if $(grep -q -- "--- FAIL:" logs/*.log); then echo "TESTS FAILED SEE THESE LOGS:"; echo ; grep -l -- "--- FAIL:" logs/*.log; exit 1; fi. Reason: exit status 1
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• Build Artifact (available for 30 days)