Adding 0BSD and Python-2.0 to allowlist

These are both in use in chromium:
* xzutils [0] uses 0BSD and is available at https://spdx.org/licenses/0BSD
* argparse [1] uses Python-2.0 and can be found at https://spdx.org/licenses/Python-2.0

xz's provided license file needs to be updated to include the 0BSD
license, and argparse doesn't include a license file, but these are
separate issues.

[0]
https://crsrc.org/c/chrome/installer/mac/third_party/xz/README.chromium
[1]
https://source.chromium.org/chromium/chromium/src/+/main:third_party/js_code_coverage/README.chromium;l=56-72

Change-Id: Ib3671a496ac4819db80c844bd15e5f4bf0da9160
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/6188506
Commit-Queue: Jordan Brown <rop@google.com>
Reviewed-by: Jordan Brown <rop@google.com>
Reviewed-by: Bill Wendling <morbo@google.com>

metadata/fields/custom/license_allowlist.py

@@ -54,6 +54,7 @@ ALLOWED_SPDX_LICENSES = frozenset([
     # go/keep-sorted end
     # permissive.
     # go/keep-sorted start case=no
+    "0BSD",
     "GPL-2.0-with-autoconf-exception",
     "GPL-2.0-with-classpath-exception",
     "GPL-3.0-with-autoconf-exception",
@@ -92,6 +93,7 @@ ALLOWED_SPDX_LICENSES = frozenset([
     "NCSA",
     "OFL-1.1",
     "OpenSSL",
+    "Python-2.0",
     "SGI-B-2.0",
     "SunPro",
     "Unicode-3.0",