CompatHelper: bump compat for MCMCDiagnosticTools to 0.2 for package test, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the MCMCDiagnosticTools package from 0.3 to 0.3, 0.2 for package test.
This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry.
It is your responsibility to make sure that your package tests pass before you merge this pull request.

[coveralls]

Pull Request Test Coverage Report for Build 3954037489

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 95.777%

---

Totals
Change from base Build 3948502488:	0.0%
Covered Lines:	703
Relevant Lines:	734

---

💛 - Coveralls

[codecov]

Codecov Report

Base: 95.76% // Head: 95.77% // Increases project coverage by +0.01% 🎉

Coverage data is based on head (79dd99b) compared to base (2e07d21).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #65      +/-   ##
==========================================
+ Coverage   95.76%   95.77%   +0.01%     
==========================================
  Files          10       10              
  Lines         732      734       +2     
==========================================
+ Hits          701      703       +2     
  Misses         31       31              

Impacted Files	Coverage Δ
src/ess.jl	100.00% <100.00%> (ø)

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