[C++] Bump vendored date library version

[asfimport]

This fix: HowardHinnant/date#696

should let us always re-enable this test:
https://github.com/apache/arrow/blob/master/cpp/src/arrow/pretty_print_test.cc#L454-L466

Reporter: Antoine Pitrou / @pitrou
Assignee: Antoine Pitrou / @pitrou

PRs and other links:

• GitHub Pull Request #11117

_{Note: This issue was originally created as ARROW-13842. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
Issue resolved by pull request 11117
#11117