[GRASS-git] [OSGeo/grass] 99cf88: CI(deps): Update alpine Docker tag to v3.18 (#2953)

[renovate[bot]]

  Branch: refs/heads/main
  Home:   https://github.com/OSGeo/grass
  Commit: 99cf88ce8cf61673e073be2e122fe48a8326df70
      https://github.com/OSGeo/grass/commit/99cf88ce8cf61673e073be2e122fe48a8326df70
  Author: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>
  Date:   2023-06-04 (Sun, 04 Jun 2023)

  Changed paths:
    M docker/README.md
    M docker/alpine/Dockerfile

  Log Message:
  -----------
  CI(deps): Update alpine Docker tag to v3.18 (#2953)

* CI(deps): Update alpine Docker tag to v3.18

* Remove docker version table; replace with version query command

---------

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>
Co-authored-by: Markus Neteler <neteler at gmail.com>