text: Title: [BUG] Examples for request body ignored during testcase generation
  Body: **Describe the bug**
  
  Yesterday I was testing an OAS which had the following pattern `^(?=[[:ascii:]]+$)[^\/\\\s$]{1,36}$` and for some reason this caused schemathesis to ignore the examples I provided for my request body. 
  
  **To Reproduce**
  Steps to reproduce the behavior:
  
  1. Add the pattern to a header parameter.
  2. Add an example request body to one of your requests which uses said header parameter.
  3. Run schemathesis (I used CLI version)
  
  **Expected behavior**
  
  Examples being included with my testcases.
  
  **Environment (please complete the following information):**
  
  - OS: [Windows]
  - Python version: [3.11.0]
  - Schemathesis version: [3.19.5]
  - Spec version: [3.0.3]
  