fix(di): get pending probes as a copy [backport 3.14]

ddtrace/debugging/_probe/registry.py

@@ -203,7 +203,7 @@ def unregister(self, *probes: Probe) -> List[Probe]:
 
     def get_pending(self, location: str) -> List[Probe]:
         """Get the currently pending probes by location."""
-        return self._pending[location]
+        return self._pending[location].copy()
 
     def __contains__(self, probe: object) -> bool:
         """Check if a probe is in the registry."""

releasenotes/notes/fix-di-copy-pending-probes-be21850231275165.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    dynamic instrumentation: fix an issue that prevented multiple probes on the
+    same location from being instrumented.

tests/debugging/test_debugger.py

@@ -553,13 +553,16 @@ def test_debugger_multiple_function_probes_on_same_lazy_module():
         for i in range(3)
     ]
 
+    sys.modules.pop("tests.submod.stuff", None)
+
     with debugger() as d:
         d.add_probes(*probes)
 
         import tests.submod.stuff  # noqa:F401
 
         assert len(d._probe_registry) == len(probes)
         assert all(_.error_type is None for _ in d._probe_registry.values())
+        assert len(d._probe_registry._pending) == 0
 
 
 # DEV: The following tests are to ensure compatibility with the tracer