fix: re-add py.typed package data, which had been erroneously removed [backport 1.15] (#6141)

Backport 75bde80 from #6115 to 1.15.

Fixes #6109

Co-authored-by: Emmett Butler <[email protected]>

Author: github-actions[bot]

releasenotes/notes/pytyped-1a3fed96165afef1.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    This fix resolves an issue causing MyPy linting to fail on files that import ddtrace.

setup.py

@@ -424,6 +424,7 @@ def get_exts_for(name):
     license="BSD",
     packages=find_packages(exclude=["tests*", "benchmarks"]),
     package_data={
+        "ddtrace": ["py.typed"],
         "ddtrace.appsec": ["rules.json"],
         "ddtrace.appsec.ddwaf": [os.path.join("libddwaf", "*", "lib", "libddwaf.*")],
     },