[2.0]: dont use non-standard modifiers in patterns

[jkowalleck]

https://json-schema.org/understanding-json-schema/reference/regular_expressions
mentions to use only common/standard regex features

this means, to not use any modifiers

• non-capturing groups (?:foo)
• and any other modifiers - https://www.regular-expressions.info/refmodifiers.html

things to fix:

• specification/schema/2.0/model/cyclonedx-common-2.0.schema.json

  Line 139 in 2a86067

  "pattern": "^(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=)?$",

• to be continued