contrib: install Python 3.9.0
We update the Windows and Linux environments to install CPython 3.9.0,
which was released a few days ago.
Differential Revision: https://phab.mercurial-scm.org/D9186
fixbundle() {
grep -v 'saving bundle' | grep -v 'saved backup' | \
grep -v added | grep -v adding | \
grep -v "unable to find 'e' for patching" | \
grep -v "e: No such file or directory" | \
cat
}