tools/generate_json_schema.py breaks when importing two schemas having same $defs

in !5974 (merged) we hit the following error:

[CONFLICT] schema are both defining '$defs/clean-name' with different content

This is because two charts both define clean-name.

What is wrong is the "with different content".

Adding some debug logging, we see this:

[CONFLICT] schema are both defining '$defs/clean-name' with different content
 {'anyOf': [
 {'type': 'string', 'pattern': '^[a-z0-9]([-a-z0-9]*[a-z0-9])?$'},
 {'$ref': '#/$defs/string-with-gotpl'}, {'type': 'null'}]
 }
vs
 {'type': 'string', 'pattern': '^[a-z0-9]([-a-z0-9]*[a-z0-9])?$'}

the difference comes from the insertion, by tools/generate_json_schema.py itself, of the anyOf/string-with-gotpl thing