containers: Run unit tests with Unicode locale

This avoids nasty UnicodeEncodeErrors and friends from our tools; while
they could be worked around with lots of manual encodings and using
binary data everywhere, this makes things unwieldy and error prone, and
would have the same net effect.

containers/unit-tests/run.sh

@@ -3,6 +3,8 @@
 set -o pipefail
 set -eux
 
+export LANG=C.UTF-8
+
 # HACK: Something invoked by our build system is setting stdio to non-blocking.
 # Validate that this isn't the surrounding context. See more below.
 python -c "import fcntl, os; assert fcntl.fcntl(0, fcntl.F_GETFL) & os.O_NONBLOCK == 0; assert fcntl.fcntl(1, fcntl.F_GETFL) & os.O_NONBLOCK == 0; assert fcntl.fcntl(2, fcntl.F_GETFL) & os.O_NONBLOCK == 0"