Fix sdist package getting wrong name

Should fix this release attempt failure.
https://github.com/pypdfium2-team/pypdfium2/actions/runs/6827951737
It failed during testpypi upload because the sdist package erroneously
got the name "pypdfium2_helpers":

Unfortunately, release commit and tag had already been published. This
has been undone by force push.

setup.py

@@ -90,7 +90,8 @@ def run_setup(modnames, pl_name, pdfium_ver):
         install_requires = [],
     )
 
-    if modnames == [ModuleHelpers]:
+    if modnames == [ModuleHelpers] and pl_name != ExtPlats.none:
+        # do not do this for sdist (none)
         kwargs["name"] += "_helpers"
         kwargs["description"] += " (helpers module)"
         kwargs["install_requires"] += ["pypdfium2_raw"]
@@ -112,7 +113,7 @@ def run_setup(modnames, pl_name, pdfium_ver):
     if ModuleRaw in modnames:
         kwargs["package_dir"]["pypdfium2_raw"] = "src/pypdfium2_raw"
 
-    if ModuleRaw not in modnames:
+    if ModuleRaw not in modnames or pl_name == ExtPlats.none:
         kwargs["exclude_package_data"] = {"pypdfium2_raw": PLATFILES_GLOB}
         if pl_name == ExtPlats.none:
             kwargs["license_files"] += LICENSES_SDIST
@@ -142,7 +143,7 @@ def main():
 
     # NOTE in principle, it may be possible to achieve the same as `prepared!` by just filling the data/ cache manually, but this is more explicit, formally disabling the generating code paths
     with_prepare, pl_name, pdfium_ver, use_v8 = parse_pl_spec(pl_spec)
-    modnames = parse_modspec(modspec, pl_name)
+    modnames = parse_modspec(modspec)
 
     if ModuleRaw in modnames and with_prepare:
         prepare_setup(pl_name, pdfium_ver, use_v8)

setupsrc/pypdfium2_setup/packaging_base.py

@@ -70,7 +70,7 @@ class SysNames:
 class ExtPlats:
     sourcebuild = "sourcebuild"
     system = "system"
-    none = "none"
+    none = "none"  # FIXME rename to sdist?
     auto = "auto"
 
 # TODO align with either python or google platform names?
@@ -554,16 +554,11 @@ def parse_pl_spec(pl_spec, need_prepare=True):
     return need_prepare, pl_name, req_ver, use_v8
 
 
-def parse_modspec(modspec, pl_name):
+def parse_modspec(modspec):
     if modspec:
         modnames = modspec.split(",")
         assert set(modnames).issubset(ModulesAll)
         assert len(modnames) in (1, 2)
     else:
         modnames = ModulesAll
-
-    modnames = list(modnames)
-    if pl_name == ExtPlats.none and ModuleRaw in modnames:
-        modnames.remove(ModuleRaw)
-
     return modnames