Ensure messages returned for metricity data do not match all excluded channels

[ChrisLovering]

The logic here was wrong due to the != requiring us to use negative logic. This meant that messages in excluded channels were still being used for message count.

Tests with my user:

SELECT
    COUNT(*)
FROM messages
WHERE
    author_id = '126811506632294400'
    AND NOT is_deleted

>>> 111,045

SELECT
    COUNT(*)
FROM messages
WHERE
    author_id = '126811506632294400'
    AND NOT is_deleted
    AND channel_id != ANY('{267659945086812160,607247579608121354}')

>>> 111,045

SELECT
    COUNT(*)
FROM messages
WHERE
    author_id = '126811506632294400'
    AND NOT is_deleted
    AND channel_id != ALL('{267659945086812160,607247579608121354}')

>>> 110,402

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[coveralls]

coverage: 100.0%. remained the same when pulling 3bec3c32dea8ebb939f7e65916905161d8ded30c on fix-metricity-message-counts into f4d4fa7af2f99ef6215fe2a86d62e8cf8f9737c5 on main.