paragraphs_library_update_8103 does not check if paragraphs_library is in the enforced modules before being added [#3471069]

Problem/Motivation

If paragraphs_library_update_8103 is run multiple times, the config key `dependencies.enforced.modules` contains multiple copies of `- paragraphs_library` under the enforced modules. These update functions normally don't run multiple times on a single site, but I have a multisite case where it did.

Steps to reproduce

Run update on a site that needed the update.
Import configuration on another site that needs to run the update.
Run the update again

Proposed resolution

Add a check before adding module list to dependencies.
Perhaps add another update function to remove duplicate entries on sites?

Remaining tasks

User interface changes

API changes

Data model changes

Comment	File	Size	Author
#5	prevent_duplicate_dependencies-3471069-5.patch	869 bytes	lallen
#3	prevent_duplicate_dependencies-3471069-3.patch	761 bytes	lallen

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3471069-avoid-duplicate-enforced-modules changes, plain diff MR !246
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3471069-paragraphslibraryupdate8103-does-not changes, plain diff MR !143
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