Add PyPDF2 to module mapping (#13717)

Important links:
- https://github.com/mstamy2/PyPDF2
- https://pypistats.org/packages/pypdf2

src/python/pants/backend/python/dependency_inference/default_module_mapping.py

@@ -73,6 +73,7 @@
     "protobuf": ("google.protobuf",),
     "pycrypto": ("Crypto",),
     "pyopenssl": ("OpenSSL",),
+    "pypdf2": ("PyPDF2",),
     "python-dateutil": ("dateutil",),
     "python-docx": ("docx",),
     "python-dotenv": ("dotenv",),