fix(symdb): switch _shallow to shallow in install (#13522)

This fixes a bug introduced by
#12957 where the shallow mode
for SymDB was introduced.

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## Reviewer Checklist
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(cherry picked from commit 58bd69c)

Author: tylfin

ddtrace/internal/symbol_db/symbols.py

@@ -668,5 +668,5 @@ def _upload_context(context: ScopeContext) -> None:
 
     @classmethod
     def install(cls, shallow=True):
-        cls._shallow = shallow
+        cls.shallow = shallow
         return super().install()

releasenotes/notes/fix-symdb-uploads-cfff7f4d568ff882.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    dynamic instrumentation: fixes an issue where only module scopes were being uploaded,
+    preventing method probes from being created.

tests/internal/symbol_db/test_symbols.py

@@ -270,7 +270,8 @@ def _upload_context(context):
 
     SymbolDatabaseUploader._upload_context = staticmethod(_upload_context)
 
-    SymbolDatabaseUploader.install()
+    SymbolDatabaseUploader.install(shallow=False)
+    assert SymbolDatabaseUploader.shallow is False
 
     def get_scope(contexts, name):
         for context in (_.to_json() for _ in contexts):