Severity-based validates_start_with_lowercase doesn't support disabling the check

[auramagi]

New Issue Checklist

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Describe the bug

• Since 0.52.1 (Let validates_start_with_lowercase option in name configurations expect a severity #4970) the boolean setting for validates_start_with_lowercase is deprecated in favor of a severity-based setting
• The default setting is error, so in spite of release notes saying that Not setting it disables the check, not setting it will in fact enable the check and result in errors on triggering lines
• The effect of validates_start_with_lowercase: false is now impossible to be achieved in a non-deprecated way

[SimplyDanny]

Hm ... what would be a good semantic here to support disabling the check without the deprecation warning? I see two:

• Accept warning, error and no/off where no/off disables the check
• Accept false without a deprecation warning

And honestly, I don't like any of these much.

[Zim999]

off makes most sense to me