[DOCS] Change name of tomlmod serializer

[pjuelsgaard]

Description
It is confusing , when met with the error message Serializer 'tomlmod' not found., when this is the shown name in the documentation

Suggested Fix
Change the module name in th documentation to show:
toml salt.serializers.tomlmod

instead of:
tomlmod salt.serializers.tomlmod

This way, we can still see the hierarchical structure leading down to the module file (salt/serializers/tomlmod.py), but can also see the module name, as seen by salt in the virtual environment.

Type of documentation
Salt Serializer Modules Documentation

Location or format of documentation
[https://docs.saltproject.io/en/latest/ref/serializers/all/index.html]

Additional context
Running Salt 3006.9 on Ubuntu 22.04 and 24.04

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