fix(profiling): HTTP exporter tag serialisation (#9032)

Ensure that the HTTP exporter does not fail to serialise the tags.

Addresses #8996.

## 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] Risks are described (performance impact, potential for breakage,
maintainability)
- [x] Change is maintainable (easy to change, telemetry, documentation)
- [x] [Library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
are followed or label `changelog/no-changelog` is set
- [x] Documentation is included (in-code, generated user docs, [public
corp docs](https://github.com/DataDog/documentation/))
- [x] Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))
- [x] If this PR changes the public interface, I've notified
`@DataDog/apm-tees`.

## Reviewer Checklist

- [ ] Title is accurate
- [ ] All changes are related to the pull request's stated goal
- [ ] Description motivates each change
- [ ] Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- [ ] Testing strategy adequately addresses listed risks
- [ ] Change is maintainable (easy to change, telemetry, documentation)
- [ ] Release note makes sense to a user of the library
- [ ] Author has acknowledged and discussed the performance implications
of this PR as reported in the benchmarks PR comment
- [ ] Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

ddtrace/profiling/exporter/http.py

@@ -152,7 +152,7 @@ def _get_tags(
 
         tags.update(self.tags)
 
-        return ",".join(tag + ":" + value for tag, value in tags.items())
+        return ",".join(f"{tag}:{value}" for tag, value in tags.items())
 
     def export(
         self,

releasenotes/notes/fix-profiling-exporter-tags-f19c6cf93cbe1502.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    profiling: fix a bug that caused the HTTP exporter to crash when attempting to serialize tags.