Fix malformed sha tag

[mbKaleb]

Fixes #1317

Changes:

• README.md: drops the .12.0 so the snippet pins the bare commit SHA.
• readme-updater.yml: change the pattern to (GIT_TAG) [^ )]+ so it
  replaces the whole token whatever its shape (SHA or dotted version) and
  stops at the closing paren. This should prevent partial-match leftovers

Verified the new expression against both historical shapes — GIT_TAG 1.12.0)
and GIT_TAG f091…79d.12.0) each come out as GIT_TAG <new-sha>).

[COM8]

Thanks!