[gimp-macos-build] (14 commits) ...jhbuild: Up minimum Mac OS requirement to 10.12

[Jehan <jehanp src gnome org>]

Summary of changes:

  d6dff9f... Build 2.10.28 (*)
  96644b0... gtk-doc: Full path to python (*)
  6ee625b... .circleci: clean up caching (*)
  65efee6... .gitignore: exclude generated files (*)
  a62a3ad... .circleci: ensure jhbuild works (*)
  a6ebe03... .circleci: Bring webkit back into the build (*)
  900bc07... .circleci: up cache version to capture webkit (*)
  0aeba75... .circleci: Update xcode version (*)
  1d1dc30... .circleci: build gimp-help and up cache version (*)
  167a334... gtk-osx: Move jhbuild modulesets into this project (*)
  239e70c... Build Gimp 2.99 (*)
  4dc2107... Get 2.99 Build working (*)
  55f44cc... poppler: Bump to version 21.11.0 (*)
  078e905... jhbuild: Up minimum Mac OS requirement to 10.12 (*)

(*) This commit already existed in another branch; no separate mail sent