bug#54204: mumi search by date provides unexpected results

[Roman Riabenko <roman@riabenko.com>]

This report is for the instance at issues.guix.gnu.org. The hint under
the search field and the online help documentation suggest that "date:"
filter can be used to improve the search results.[1] However, the
results are different from what is documented. For example, there is a
report submitted on 16 February 2022 and a patch submitted on 20
Fenruary 2022 both contaning the word "mumi".[2][3] I can see them at
the end of search results when searching for "mumi".[4] But I cannot
find them with any of the following:

1. mumi date:20d..now
2. mumi date:2022-02-01..2022-02-28

The first one returns older posts only.[5] The second one returns
nothing.[6]

And the last hinted filter does return links to the expected issues but
also returns other issues which are apparently out of the specified
time period and so introduces noise in the search results making
filtering less effective:[7]

3. mumi date:1m..today

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[1] https://issues.guix.gnu.org/help#search
[2] https://issues.guix.gnu.org/54024
[3] https://issues.guix.gnu.org/54072
[4] https://issues.guix.gnu.org/search?query=mumi
[5] https://issues.guix.gnu.org/search?query=mumi+date%3A20d..now
[6]
https://issues.guix.gnu.org/search?query=mumi+date%3A2022-02-01..2022-02-28
[7] https://issues.guix.gnu.org/search?query=mumi+date%3A1m..today

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Roman