Recipes defining outputs without package/version fail in 3.28.0

[kenodegard]

What happened?

#5055 corrected how the metadata's version was validated and resulted in multi outputs failing to build unless they also define the top level package/version.

Xref conda-forge/admin-requests#890

Conda Details

conda info

     active environment : None
            shell level : 0
       user config file : /Users/kodegard/.condarc
 populated config files : /Users/kodegard/.condarc
          conda version : 23.11.0
    conda-build version : 3.28.0
         python version : 3.10.13.final.0
                 solver : libmamba (default)
       virtual packages : __archspec=1=m1
                          __conda=23.11.0=0
                          __osx=13.6=0
                          __unix=0=0
       base environment : /Users/kodegard/.conda/arm64/23.10.0/3.11  (writable)
      conda av data dir : /Users/kodegard/.conda/arm64/23.10.0/3.11/etc/conda
  conda av metadata url : None
           channel URLs : https://repo.anaconda.com/pkgs/main/osx-arm64
                          https://repo.anaconda.com/pkgs/main/noarch
                          https://repo.anaconda.com/pkgs/r/osx-arm64
                          https://repo.anaconda.com/pkgs/r/noarch
          package cache : /Users/kodegard/.conda/arm64/23.10.0/3.11/pkgs
                          /Users/kodegard/.conda/pkgs
       envs directories : /Users/kodegard/.conda/arm64/23.10.0/3.11/envs
                          /Users/kodegard/.conda/envs
               platform : osx-arm64
             user-agent : conda/23.11.0 requests/2.31.0 CPython/3.10.13 Darwin/22.6.0 OSX/13.6 solver/libmamba conda-libmamba-solver/23.11.1 libmambapy/1.5.3
                UID:GID : 501:20
             netrc file : None
           offline mode : False

[kenodegard]

Before #5055, where package/version (e.g., None) is cast to a string (e.g., "None") before validation:

conda-build/conda_build/metadata.py

Lines 1449 to 1452 in 923b59a

	def version(self):
	res = str(self.get_value("package/version"))
	if res is None:
	sys.exit("Error: package/version missing in: %r" % self.meta_path)

After #5055, where package/version is validated before cast to a string:

conda-build/conda_build/metadata.py

Lines 1443 to 1447 in decbcf9

	def version(self) -> str:
	version = self.get_value("package/version", "")
	if not version and self.final:
	sys.exit("Error: package/version missing in: %r" % self.meta_path)
	version = str(version)

[jezdez]

Fixed by #5096.