chore(ci_visibility): set the content type header when in EVP mode

[romainkomorndatadog]

This makes sure that the content-type header is properly set when the CI Visibility service uses the EVP proxy method for requests.

This does not, actually, fix anything since the API still responds properly without the header, so no fix release note is added.

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
• Release note makes sense to a user of the library
• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[github-actions]

CODEOWNERS have been resolved as:

ddtrace/internal/ci_visibility/recorder.py                              @DataDog/ci-app-libraries
tests/ci_visibility/test_ci_visibility.py                               @DataDog/ci-app-libraries

[datadog-dd-trace-py-rkomorn]

Datadog Report

Branch report: romain.komorn/chore/set_content_type_header_in_EVP
Commit report: 8bc2fd0
Test service: dd-trace-py

✅ 0 Failed, 578 Passed, 1624 Skipped, 5m 7.04s Total Time

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-08-27 13:13:10

Comparing candidate commit 8bc2fd0 in PR branch romain.komorn/chore/set_content_type_header_in_EVP with baseline commit ecc5741 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 353 metrics, 47 unstable metrics.