Bug#906284: lintian: check for incomplete-creative-commons-license gives false positives: the "not a law firm" is a preamble, not a license

[Jonathan Dowland]

Interestingly, 307 is roughly half of all CC-license using packages,
based on the numbers I counted in #795402

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⣾⠁⢠⠒⠀⣿⡁ Jonathan Dowland
⢿⡄⠘⠷⠚⠋⠀ https://jmtd.net
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