fixup! EmailNotification: address Use of uninitialized value in numeric eq (==)

Dependencies

• [2] 3SPKUVLJ EmailNotification: address Use of uninitialized value in numeric eq (==)
• [3] 5WNGKHLZ Plugins: Add isEnabled method
• [4] QDJRQIFF If multiple dependent builds fail, send a single email
• [*] 5EQYVRWE Add a plugin mechanism

Change contents

• replacement in src/lib/Hydra/Plugin/EmailNotification.pm at line 15
  [3.320]→[2.0:105](∅→∅)
  − return defined($self->{config}->{email_notification}) && $self->{config}->{email_notification} == 1;
  [3.320]

  [3.375]
  + return ($self->{config}->{email_notification} // 0) == 1;