Sync with 2.26.3

* maint-2.26: Git 2.26.3 Git 2.25.5 Git 2.24.4 Git 2.23.4 Git 2.22.5 Git 2.21.4 Git 2.20.5 Git 2.19.6 Git 2.18.5 Git 2.17.6 unpack_trees(): start with a fresh lstat cache run-command: invalidate lstat cache after a command finished checkout: fix bug that makes checkout follow symlinks in leading path