Hide validation count in menu when on dev tools screen, dev tools is not enabled and Reader mode is enabled

[pierlon]

Summary

Fixes #6120

Checklist

• My code is tested and passes existing tests.
• My code follows the Engineering Guidelines (updates are often made to the guidelines, check it out periodically).

[github-actions]

Plugin builds for 8f9fefd are ready 🛎️!

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[codecov]

Codecov Report

Merging #6122 (8f9fefd) into develop (f7ad0a8) will increase coverage by 0.08%.
The diff coverage is 100.00%.

@@              Coverage Diff              @@
##             develop    #6122      +/-   ##
=============================================
+ Coverage      75.03%   75.11%   +0.08%     
- Complexity      5829     5847      +18     
=============================================
  Files            232      233       +1     
  Lines          17618    17655      +37     
=============================================
+ Hits           13219    13262      +43     
+ Misses          4399     4393       -6     

Flag	Coverage Δ	Complexity Δ
javascript	79.84% <ø> (ø)	0.00 <ø> (ø)
php	74.90% <100.00%> (+0.09%)	5847.00 <0.00> (+18.00)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ	Complexity Δ
src/DevTools/UserAccess.php	100.00% <ø> (ø)	22.00 <0.00> (ø)
...s/validation/class-amp-validated-url-post-type.php	65.27% <100.00%> (+0.05%)	441.00 <0.00> (+1.00)
...validation/class-amp-validation-error-taxonomy.php	50.23% <100.00%> (+0.06%)	540.00 <0.00> (+1.00)
includes/amp-helper-functions.php	84.93% <0.00%> (ø)	0.00% <0.00%> (ø%)
includes/sanitizers/class-amp-object-sanitizer.php	100.00% <0.00%> (ø)	11.00% <0.00%> (?%)
includes/embeds/class-amp-core-block-handler.php	93.27% <0.00%> (+5.88%)	48.00% <0.00%> (+5.00%)

[westonruter]

When I turn off DevTools and manually go to /wp-admin/edit.php?post_type=amp_validated_url, before I saw:

But in this branch I see:

When I turn DevTools back on, I again see:

So it's working as expected!