key: :99 reports value as :"99" rather than ":99" - how to include second colon as part of the value string?

[jeffwidman]

Over in dependabot/dependabot-core#5453 a user reported a parsing difficulty with the following example YAML file:

env:
  DISPLAY: :99

So I tried parsing it:

irb(main):002:0> s = Psych.safe_load('env:\n  DISPLAY: :99')
# throws exception about unable to load the `Symbol` class

irb(main):002:0> s = Psych.safe_load('env:\n  DISPLAY: :99', permitted_classes: [Symbol])
=> {"env:\\n  DISPLAY"=>:"99"}

# Now try quoting the value w/o permitting Symbol:
irb(main):003:0> w = Psych.safe_load('env:\n  DISPLAY: ":99"')
=> {"env:\\n  DISPLAY"=>":99"}

# contrast the resulting values:
irb(main):006:0> s.values[0]
=> :"99"
irb(main):007:0> w.values[0]
=> ":99"

Notice that these two values differ... :"99" rather than the expected ":99, ie symbol for "99" vs full string ":99".

Is there a way to configure Psych to treat the colon as part of the string and not a symbol indicator?