Partial content-type results in GraphiQL formatting errors

[moritz89]

Describe the Bug

GraphiQL prints hidden characters:

System Information

• Operating system: Ubuntu 24.10
• Strawberry version (if applicable): 0.261.1 and 0.57.0
• Browser: Firefox 136.0.2 and Chromium 134.0.6998.117 (Official Build) snap (64-bit)

Additional Context

The bug occurs as the content-type header is not set properly. It should be set to Content-Type: text/html; charset=utf-8 instead of only Content-Type: text/html.

strawberry/channels/handlers/http_handler.py:296 --> render_graphql_ide()

[bellini666]

Fixed by #3824