Update pin for libprotobuf

[regro-cf-autotick-bot]

This PR has been triggered in an effort to update the pin for libprotobuf. The current pinned version is 5.28.3, the latest available version is 5.29.3 and the max pin pattern is x.x.x. This migration will impact 68 feedstocks.

Checklist:

• The new version is a stable supported pin.
• I checked that the ABI changed from 5.28.3 to 5.29.3.

**Please note that if you close this PR we presume that the new pin has been rejected.

@conda-forge-admin please ping libprotobuf

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[conda-forge-webservices]

Hi! This is the friendly automated conda-forge-webservice.

I was asked to ping @conda-forge/libprotobuf and so here I am doing that.

[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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[h-vetinari]

Done in #7104