chore: filter type of releases in the badge

[thomaspoignant]

Description

Readme badge for releases, filter only on version starting with v*.

Checklist

• I have tested this code
• I have updated the documentation (README.md and /website/docs)
• I have followed the contributing guide

[netlify]

✅ Deploy Preview for go-feature-flag-doc-preview canceled.

Name	Link
🔨 Latest commit	2e57c19
🔍 Latest deploy log	https://app.netlify.com/projects/go-feature-flag-doc-preview/deploys/68ef8e196cca3f0008859026

[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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.76%. Comparing base (74720e5) to head (2e57c19).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4101   +/-   ##
=======================================
  Coverage   83.76%   83.76%           
=======================================
  Files         139      139           
  Lines        6831     6831           
=======================================
  Hits         5722     5722           
  Misses        898      898           
  Partials      211      211           

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