Revert RP_SHA to fb4dd9b (last known-good for Apple Silicon)

The newer relocatable-python commit 8ee72fe (Oct 2024, adds symlink
path handling) causes ensurepip to die with SIGKILL on Apple Silicon
during the framework build: install_name_tool invalidates the
binary's code signature, and ensurepip runs before any re-sign step,
so Gatekeeper kills the process.

A prior bump attempt was already reverted in this repo (commit d8db8a2,
PR #67) — sticking with fb4dd9b until upstream addresses the
ad-hoc-resign-before-ensurepip flow.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

build_python_framework_pkgs.zsh

@@ -9,7 +9,7 @@
 set -eu
 
 # --- Pinned upstream commits ---
-RP_SHA="8ee72fe3a5dbef733365370ebf44f25022b895ef"  # gregneagle/relocatable-python
+RP_SHA="fb4dd9b024b249c71713f14d887f4bcea78aa8b0"  # gregneagle/relocatable-python
 MP_SHA="bbd07730d1b93ed3828246575ef5676bba74b5d1"  # munki/munki-pkg
 
 # --- Paths and constants ---