Close out migration for proxsuite071

[olivier-roussel]

Following the discussion in #6998.
Proxsuite 0.7.1 migration is now done for a while ( https://conda-forge.org/status/migration/?name=proxsuite071 ) so this PR closes the migration and adds proxsuite 0.7.1 to global pinning.

Checklist

• Used a personal fork of the feedstock to propose changes

[conda-forge-admin]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe/meta.yaml) and found it was in an excellent condition.

I do have some suggestions for making it better though...

For recipe/meta.yaml:

• ℹ️ top-level output has some malformed specs:

• In section test: python >= 3.8 Requirements spec fields should always be space-separated to avoid known issues in conda-build. For example, instead of name =version=build, use name version build`.

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