Fix #9672: Artifact Schema Check

[aranke]

resolves #9672

Problem

Artifact schema check was failing and was running on all PRs

Solution

1. Run only on PRs that change core/dbt/artifacts directory
2. Upload artifact schema_changes.txt in case there is a failing run.

Example runs:

1. Fail – https://github.com/dbt-labs/dbt-core/actions/runs/8910440719
2. Skip – https://github.com/dbt-labs/dbt-core/actions/runs/8910475178

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX
• This PR includes type annotations for new and modified functions

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.19%. Comparing base (a36057d) to head (a1376e4).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10069      +/-   ##
==========================================
+ Coverage   88.17%   88.19%   +0.01%     
==========================================
  Files         181      181              
  Lines       22700    22700              
==========================================
+ Hits        20016    20020       +4     
+ Misses       2684     2680       -4     

Flag	Coverage Δ
integration	85.57% <ø> (+0.08%)	⬆️
unit	62.34% <ø> (ø)

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