[repo] Update stale.yml - reduce days before stale to 450

[TimothyMothra]

Follow up to #5776

The ultimate goal is to get this down to 300 days.
This PR moves the days-before-issue-stale from 600 to 450 days and split the remaining issues in half.

Counts of issues

• Currently 260 open issues (Oct 07, 2024).
• older than 450 days (07/15) = 38 issues link
• older than 300 days (12/12) = 73 issues link

Screenshot of affected issues

Click here to expand

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.35%. Comparing base (6250307) to head (52b3877).
Report is 340 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5888      +/-   ##
==========================================
+ Coverage   83.38%   86.35%   +2.97%     
==========================================
  Files         297      257      -40     
  Lines       12531    11214    -1317     
==========================================
- Hits        10449     9684     -765     
+ Misses       2082     1530     -552     

Flag	Coverage Δ
unittests	?
unittests-Project-Experimental	86.17% <ø> (?)
unittests-Project-Stable	86.25% <ø> (?)
unittests-Solution	86.15% <ø> (?)
unittests-UnstableCoreLibraries-Experimental	85.68% <ø> (?)

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

see 234 files with indirect coverage changes

[CodeBlanch]

LGTM