bump version to 9.0.0

[kp-cat]

Requirement checklist (only if applicable)

• I have covered the applied changes with automated tests.
• I have executed the full automated test set against my changes.
• I have validated my changes against all supported platform versions.
• I have read and accepted the contribution agreement.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 98.52%. Comparing base (734db70) to head (04eb5f9).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
lib/configcat/version.rb	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #42      +/-   ##
==========================================
- Coverage   98.69%   98.52%   -0.18%     
==========================================
  Files          39       40       +1     
  Lines        3290     3314      +24     
==========================================
+ Hits         3247     3265      +18     
- Misses         43       49       +6     

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