persistent_tasks: suppress logs from Pkg.jl

[aviatesk]

By using io=devnull option, which is only available in Julia 1.9 and above.

[codecov[bot]]

Codecov Report

Attention: 7 lines in your changes are missing coverage. Please review.

Comparison is base (e9a4230) 75.33% compared to head (797ab09) 70.68%.

Files	Patch %	Lines
src/persistent_tasks.jl	0.00%	7 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #256 +/- ## ========================================== - Coverage 75.33% 70.68% -4.66% ========================================== Files 11 11 Lines 750 747 -3 ========================================== - Hits 565 528 -37 - Misses 185 219 +34 ``` | [Flag](https://app.codecov.io/gh/JuliaTesting/Aqua.jl/pull/256/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaTesting) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/JuliaTesting/Aqua.jl/pull/256/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaTesting) | `70.68% <0.00%> (-4.66%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaTesting#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[lgoettgens]

Thanks for your PR! The whole test is only run for julia 1.10 and later (see https://github.com/JuliaTesting/Aqua.jl/pull/256/files#diff-f727412b094adb6463b973046def5a3004e1e292aca989b8b4564ce26f5132feR121), so you don't need all of these @static if everywhere.

[aviatesk]

Thanks for your review! Updated.