Please describe the problem.

started to happen in https://github.com/datalad/git-annex/actions/runs/750505573

looked only at "normal" run ``` export_import: FAIL (0.93s) ./Test/Framework.hs:57: export to dir failed (transcript follows) export foo bar.c okexport foo foo /home/runner/.t/tmprepo4/dir/foo6874-4.tmp: openBinaryFile: resource busy (file is locked)failedexport foo sha1foo /home/runner/.t/tmprepo4/dir/sha1foo6874-7.tmp: openBinaryFile: resource busy (file is locked)failed(recording state in git...)git-annex: export: 2 failed

export_import:                                        FAIL (0.58s)
  ./Test/Framework.hs:57:
  export to dir failed (transcript follows)
  export foo bar.c okexport foo foo   /home/runner/.t/tmprepo98/dir/foo45594-4.tmp: openBinaryFile: resource busy (file is locked)failedexport foo sha1foo   /home/runner/.t/tmprepo98/dir/sha1foo45594-7.tmp: openBinaryFile: resource busy (file is locked)failed(recording state in git...)git-annex: export: 2 failed

... export_import: FAIL (0.52s) ./Test/Framework.hs:57: export to dir failed (transcript follows) export foo bar.c okexport foo foo /home/runner/.t/tmprepo192/dir/foo75699-4.tmp: openBinaryFile: resource busy (file is locked)failedexport foo sha1foo /home/runner/.t/tmprepo192/dir/sha1foo75699-7.tmp: openBinaryFile: resource busy (file is locked)failed(recording state in git...)git-annex: export: 2 failed ```

so actually looks like the same test in various scenarios.

probably relates to the tune ups to make importtree work with CoW

fixed --Joey