Add linecache, difflib, gc to UNSAFE_IMPORTS (GHSA-r48f-3986-4f9c)

linecache and difflib could access arbitrary files, and gc
can give references to tracked unsafe modules.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: thomas-chauchefoin-tob

fickling/fickle.py

@@ -69,6 +69,7 @@
         "_imp",
         "pkgutil",
         "zipimport",
+        "gc",
         # Attribute access (getattr equivalent bypasses)
         "inspect",
         # Operator module bypasses
@@ -141,6 +142,8 @@
         "fileinput",
         "glob",
         "platform",
+        "linecache",
+        "difflib",
         # Code compilation (writes .pyc files)
         "compileall",
         "py_compile",