Support multiple outputs in pytorch parser

[JanFSchulte]

Fixes the issue reported in #1147 that the pytorch parser was not able to handle multiple outputs and would just use the last node as the output layer.

Type of change

• Bug fix (non-breaking change that fixes an issue)

-## Tests

Tested the example model provided in #1147, which fails to produce the correct output before this PR and is successful after this fix.

Checklist

• I have read the guidelines for contributing.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have installed and run pre-commit on the files I edited or added.
• I have added tests that prove my fix is effective or that my feature works.

[JanFSchulte]

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