fa4cb13 test: [doc] Manually unify stale headers (MarcoFalke)
fa5f297 scripted-diff: [doc] Unify stale copyright headers (MarcoFalke)

Pull request description:

  Historically, the upper year range in file headers was bumped manually
  or with a script.

  This has many issues:

  * The script is causing churn. See for example commit 306ccd4, or
    drive-by first-time contributions bumping them one-by-one. (A few from
    this year: #32008,
    #31642,
    #32963, ...)
  * Some, or likely most, upper year values were wrong. Reasons for
    incorrect dates could be code moves, cherry-picks, or simply bugs in
    the script.
  * The upper range is not needed for anything.
  * Anyone who wants to find the initial file creation date, or file
    history, can use `git log` or `git blame` to get more accurate
    results.
  * Many places are already using the `-present` suffix, with the meaning
    that the upper range is omitted.

  To fix all issues, this bumps the upper range of the copyright headers
  to `-present`.

  Further notes:

  * Obviously, the yearly 4-line bump commit for the build system (c.f.
    b537a2c) is fine and will remain.
  * For new code, the date range can be fully omitted, as it is done
    already by some developers. Obviously, developers are free to pick
    whatever style they want. One can list the commits for each style.
  * For example, to list all commits that use `-present`:
    `git log --format='%an (%ae) [%h: %s]' -S 'present The Bitcoin'`.
  * Alternatively, to list all commits that use no range at all:
    `git log --format='%an (%ae) [%h: %s]' -S '(c) The Bitcoin'`.

  <!--
  * The lower range can be wrong as well, so it could be omitted as well,
    but this is left for a follow-up. A previous attempt was in
    #26817.

ACKs for top commit:
  l0rinc:
    ACK fa4cb13
  rkrux:
    re-ACK fa4cb13
  janb84:
    ACK fa4cb13

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