docs: say what archived means on the RetroPie page

The RetroPie guide note still tied the archived status to a scraping
schedule no tool runs. The doc test now reads _guides.yml too.

platforms/_guides.yml

@@ -648,8 +648,8 @@ guides:
       RetroPie also installs standalone emulators (openMSX, PCSX2, XRoar, Amiberry and
       others) whose files only the RetroPie file list carries.
     - >-
-      RetroPie is archived in this project: its configuration is kept and the command
-      serves it, but its upstream list is no longer read again on a schedule.
+      RetroPie is archived in this project: the command serves it, and checks that cover
+      every setup include it only on request.
     pack_manual: |
       Option B: Via network share
       --------------------------

tests/test_doc_pages.py

@@ -1918,6 +1918,7 @@ class ArchivedIsWhatTheToolsDo(unittest.TestCase):
             "generate_site": inspect.getsource(generate_site),
             "generate_pack": inspect.getsource(generate_pack),
             "list_platforms": inspect.getsource(list_platforms),
+            "_guides.yml": (ROOT / "platforms" / "_guides.yml").read_text(encoding="utf-8"),
         }
         for name, text in texts.items():
             with self.subTest(name):