(GH-1115) Bump json_pure to ~> 2.5.1 on Ruby >= 2.7

[sanfrancrisko]

See also puppetlabs/pdk-vanagon#292

Closes: #1115

[codecov]

Codecov Report

Merging #1124 (6d877d5) into main (18754e5) will not change coverage.
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[sanfrancrisko]

Tests:

• bundle install using Ruby < 2.7 installs json_pure 2.1.0
• bundle install using Ruby >= 2.7 installs json_pure 2.5.1
• Removes warnings when running with json_pure 2.5.1 on Ruby 2.7 (see below)
• pdk validate metadata (using json_pure 2.5.1) does not flag issues for valid metadata.json
• pdk validate metadata (using json_pure 2.5.1) flags invalid metadata.json

---

json_pure 2.5.1 on Ruby 2.7:

~/bin/pdk validate metadata
pdk (WARN): This module is compatible with an older version of PDK. Run `pdk update` to update it to your version of PDK.
pdk (INFO): Using Ruby 2.7.3
pdk (INFO): Using Puppet 7.8.0
┌ [✔] Running metadata validators ...
├── [✔] Checking metadata syntax (metadata.json tasks/*.json).
└── [✔] Checking module metadata style (metadata.json).

[RandomNoun7]

Hi Content Team. I don't think this PR actually worked for at least one use case. When specifying PDK as a dependency in a module's Gemfile, the version of json_pure added to the Bundle is still 2.1.0. I think the reason is that Rubygems doesn't know how to add conditional runtime dependencies. You can see in the Rubygems page for pdk that the json_pure dependency is still listed as 2.1.0

The Puppet team ran into this issue and had to use a workaround as well because of the Rubygems not doing conditionals problem https://tickets.puppetlabs.com/browse/PUP-10797

The only thing I know worked in my testing was to add a specific entry for json_pure to the Gemfile status specifically that it must be >= 2.3.0.

I also found that just removing PDK from my Gemfile worked, and I don't know why it was there in the first place, but the fact remains that I don't think Rubygems has picked up the fix in this PR as intended.