fix[stac_fastapi.core]: await request.body() coroutine (#551)

**Related Issue(s):**
N/A

**Description:**
Fixes an unawaited coroutine:

```
stac_fastapi/core/core.py:762: RuntimeWarning: coroutine 'Request.body' was never awaited
  if request.method == "POST" and request.body():
```

`request.body()` always had a bool value of `True` as it is the
coroutine, not the result.

**PR Checklist:**

- [x] Code is formatted and linted (run `pre-commit run --all-files`)
- [x] Tests pass (run `make test`)
- [ ] Documentation has been updated to reflect changes, if applicable
- [x] Changes are added to the changelog

Author: StijnCaerts

CHANGELOG.md

@@ -13,6 +13,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ### Fixed
 
+- Fix unawaited coroutine in `stac_fastapi.core.core`. [#551](https://github.com/stac-utils/stac-fastapi-elasticsearch-opensearch/pull/551)
+
 ### Removed
 
 ### Updated

stac_fastapi/core/stac_fastapi/core/core.py

@@ -759,7 +759,7 @@ async def post_search(
 
         body_limit = None
         try:
-            if request.method == "POST" and request.body():
+            if request.method == "POST" and await request.body():
                 body_data = await request.json()
                 body_limit = body_data.get("limit")
         except Exception: