[doc] Fix typo in old Doctrine Annotation syntax

[cvergne]

The text was displaying the Attribute syntax instead of the Doctrine Annotation syntax.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.81%. Comparing base (53f9d49) to head (ea09029).
⚠️ Report is 137 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #787      +/-   ##
============================================
- Coverage     95.72%   94.81%   -0.91%     
- Complexity     1773     1851      +78     
============================================
  Files           154      175      +21     
  Lines          4586     4883     +297     
============================================
+ Hits           4390     4630     +240     
- Misses          196      253      +57     

☔ 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.

[oojacoboo]

Thanks @cvergne!