Unquoted float-format `variables:` values result in an ambiguous syntax error

It seems float-format (single-dotted) variables: values are improperly… parsed (?) resulting in an error, unless quoted. The ‘quotation’ of variable values is not explicitly stated in the docs (as far as my search goes). Adding another dot to the value makes the syntax check pass.

Failing scenario (applies for GitLab.com as well as self hosted 14.8.2-ee / 14.7.4-ee):

variables:
  SOME_VAR: 0.9

job:
  script:
  - echo 1

Quoted values or unquoted values with more dots do work:

variables:
  SOME_VAR: 0.9.

job:
  script:
  - echo 1

image

variables:
  SOME_VAR: '0.9'

job:
  script:
  - echo 1

image

In all cases I’d expect for no error to occur. All values should be valid, quoted or not, independently from their length. Either this or value quoting should be mandatory to avoid confusion (since it seems all values are treated as strings anyways).

Is this an expected behaviour, did I miss anything in the docs or should I report a bug?