catch ValueError on changed = "latest"

[aagbsn]

When parsing the all_as_org_map:
https://archive.org/download/ip2country-as/all_as_org_map.json
produced by https://github.com/ooni/historical-geoip/blob/main/build_all_as_org_map.py
the upstream data source has included "latest" for the "changed" field rather than a specific day.

This metadata probably does not affect the behavior of clients, but this has not been verified.

This changes the updater to accept "latest" as a value.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.86%. Comparing base (17a4258) to head (43c5de7).

❗ There is a different number of reports uploaded between BASE (17a4258) and HEAD (43c5de7). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (17a4258)	HEAD (43c5de7)
oonipipeline	1	0

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #165      +/-   ##
==========================================
- Coverage   84.06%   77.86%   -6.20%     
==========================================
  Files          85       33      -52     
  Lines        5271     1938    -3333     
==========================================
- Hits         4431     1509    -2922     
+ Misses        840      429     -411     

Flag	Coverage Δ
oonidata	77.86% <ø> (ø)
oonipipeline	?

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[aagbsn]

this is broken and needs a date value because consumer of this table orders by changed;