Disable loading .env file when running foreman for development

[Flixt]

TL;DR;

This PR fixes the problem that when a RAILS_MASTER_KEY is defined with the key for production in .env (which is the case when using Kamal for deployment), the script in bin/dev will start foreman which will then pick up the variables from .env leading to a ActiveSupport::MessageEncryptor::InvalidMessage error when running bin/dev

Kamal is added by default for new Rails apps >= v8 (see rails/rails#51798). Although, it seems that is not fully initialized and the .env file generated by kamal init is removed when a new Rails app is generated.

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There are several other problems with the .env approach of Kamal, so I'm not entirely sure if this PR is the "correct" fix, but is seems reasonable as bin/dev is only run locally to start bundling + rails.

See other:

• procfile causes failure on Rails 8.0 rails#51829 (Original issue/PR leading to this PR)
• .env load behaviour at odds with dotenv ddollar/foreman#702 (Foreman issue describing the --env /dev/null solution)
• `config/deploy.production.yml` should be default behavior, rather than `config/deploy.yml` basecamp/kamal#617 (Discussion explaining why .env in Kamal is dangerous)
• load environment variables from multiple .env files as dotenv-rails basecamp/kamal#233 (Issue about supporting multiple environments in Kamal)
• Foreman & MRSK incompatibility – best way to approach? basecamp/kamal#420 (Another discussion about Foreman & Kamal/MRSK incompatibility)