install.sh: set LC_ALL=en_US.UTF-8 on python3 thunk
install.sh: set LC_ALL=en_US.UTF-8 on python3 thunk

scylla-python3 causes segfault when non-default locale specified.
As workaround for this, we need to set LC_ALL=en_US.UTF_8 on python3 thunk.

Fixes #7408

Closes #7414

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla