v2.1.2

Fixed

• The action announced the wrong version of itself. 2.1.1 printed
  v2.1.0 on every run and, more consequentially, stamped 2.1.0 as
  the SARIF tool version, so GitHub code scanning filed findings under a
  release that never contained the code that produced them. The constant
  is hand-kept; nothing compared it to the changelog. Now something
  does: the end-to-end suite fails when the declared version, the run
  banner and the SARIF tool version disagree with the newest changelog
  entry.