Multi-Project pipeline with `needs:pipeline` using example from docs results in undefined error

Summary

Using the example in the documention for Mirroring status from upstream pipeline

upstream_bridge:
  stage: test
  needs:
    pipeline: other/project

results in an "undefined error"

Example Project

You can view this on gitlab.com in a test project of mine: https://gitlab.com/kevenhughes/arcport/pipelines/81165861

Replicated on self-managed 12.2.4-ee as well.

Relevant logs and/or screenshots

production.log:

Completed 500 Internal Server Error in 53ms (ActiveRecord: 7.7ms | Elasticsearch: 0.0ms)
  
NoMethodError (undefined method `to_sym' for [:pipeline, "other/project"]:Array
Did you mean?  to_s
               to_set):
  
lib/gitlab/ci/yaml_processor.rb:164:in `block in validate_job_needs!'
lib/gitlab/ci/yaml_processor.rb:163:in `each'
lib/gitlab/ci/yaml_processor.rb:163:in `validate_job_needs!'
lib/gitlab/ci/yaml_processor.rb:113:in `block in initial_parsing'
lib/gitlab/ci/yaml_processor.rb:108:in `each'
lib/gitlab/ci/yaml_processor.rb:108:in `initial_parsing'
lib/gitlab/ci/yaml_processor.rb:20:in `initialize'
lib/gitlab/ci/yaml_processor.rb:87:in `new'
lib/gitlab/ci/yaml_processor.rb:87:in `validation_message'

Possible fixes

using to_sym on an array is invalid:

irb(main):009:0> ar = ["one", 2, 3.0]
=> ["one", 2, 3.0]
irb(main):010:0> ar.to_sym
Traceback (most recent call last):
        4: from /usr/local/bin/irb:23:in `<main>'
        3: from /usr/local/bin/irb:23:in `load'
        2: from /usr/local/lib/ruby/gems/2.6.0/gems/irb-1.0.0/exe/irb:11:in `<top (required)>'
        1: from (irb):10
NoMethodError (undefined method `to_sym' for ["one", 2, 3.0]:Array)
Did you mean?  to_s
               to_set

relevant lines of code:

https://gitlab.com/gitlab-org/gitlab-ee/blob/v12.2.0-ee/lib/gitlab/ci/yaml_processor.rb#L164

Customer ticket: https://gitlab.zendesk.com/agent/tickets/131433 (internal)