fix(asm): fix 403 response being inadequatly replaced by datadog response block response (1.9) (#5328)

Fix 403 response being inadequatly replaced by datadog response block
response in 1.9 branch.

This bug was automatically fixed in 1.10rc2 by suspicious request
blocking PRs.

Patch to solve tickets #1131460 and #1132841

## Checklist

- [x] Change(s) are motivated and described in the PR description.
- [x] Testing strategy is described if automated tests are not included
in the PR.
- [x] Risk is outlined (performance impact, potential for breakage,
maintainability, etc).
- [x] Change is maintainable (easy to change, telemetry, documentation).
- [x] [Library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/contributing.html#Release-Note-Guidelines)
are followed.
- [x] Documentation is included (in-code, generated user docs, [public
corp docs](https://github.com/DataDog/documentation/)).
- [x] Author is aware of the performance implications of this PR as
reported in the benchmarks PR comment.

## Reviewer Checklist

- [x] Title is accurate.
- [x] No unnecessary changes are introduced.
- [x] Description motivates each change.
- [x] Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes unless absolutely necessary.
- [x] Testing strategy adequately addresses listed risk(s).
- [x] Change is maintainable (easy to change, telemetry, documentation).
- [x] Release note makes sense to a user of the library.
- [x] Reviewer is aware of, and discussed the performance implications
of this PR as reported in the benchmarks PR comment.

Author: christophe-papazian

ddtrace/contrib/django/patch.py

@@ -384,7 +384,11 @@ def traced_get_response(django, pin, func, instance, args, kwargs):
                     )
                 else:
                     response = func(*args, **kwargs)
-                    if isinstance(response, HttpResponseForbidden):
+                    if (
+                        config._appsec_enabled
+                        and _context.get_item("http.request.blocked", span=span)
+                        and isinstance(response, HttpResponseForbidden)
+                    ):
                         # Add our custom block template
                         response.content = appsec_utils._get_blocked_template(request_headers.get("Accept"))
                 return response

releasenotes/notes/asm_fix_403_django_body-9adabde1f2f95c98.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    ASM: This fix resolves an issue where some 403 body responses in Django where wrongly replaced by datadog 403 block response body.