fix: response content-type value amount as one with testcase

[PoChenKuo]

Discussion #1697 [link]

Mechanism

Response header's contentType

Content-Type should be a single value(string) for header's response.

Checklist

• [* ] I have ensured my pull request is not behind the main or master branch of the original repository.
• [* ] I have rebased all commits where necessary so that reviewing this pull request can be done without having to merge it first.
• [* ] I have written a commit message that passes commitlint linting.
• [* ] I have ensured that my code changes pass linting tests.
• [* ] I have ensured that my code changes pass unit tests.
• [* ] I have described my pull request and the reasons for code changes along with context if necessary.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.90%. Comparing base (cb22d8d) to head (28cf130).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1899   +/-   ##
=======================================
  Coverage   99.90%   99.90%           
=======================================
  Files           9        9           
  Lines        2048     2067   +19     
=======================================
+ Hits         2046     2065   +19     
  Misses          2        2           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.