Respect GRANIAN_WORKERS env var in production

[tartansandal]

Ensures that GRANIAN_WORKERS environment variable is not overridden by --workers parameter when starting the production server.

While testing docker containers on my laptop, I was surprised that I was getting 41 workers when I had set GRANIAN_WORKERS=1. Had to use the deprecated GUNICORN_WORKERS env var to work around this.

I'm not sure if the fix is in the right place, with the config and setup code in flux with the move to granian and 0.8.0, but it does solve the immediate problem.

[greptile-apps]

PR Summary

Fixes production server worker configuration to respect the GRANIAN_WORKERS environment variable, preventing it from being overridden by the automatic worker calculation.

• Modified reflex/utils/exec.py to only apply calculated worker count when GRANIAN_WORKERS is not set
• Resolves issue where Docker containers would ignore user-specified worker counts
• Particularly relevant for development environments where lower worker counts may be desired

_{💡 (1/5) You can manually trigger the bot by mentioning @greptileai in a comment!}

_{1 file(s) reviewed, no comment(s)
Edit PR Review Bot Settings | Greptile}

[codspeed-hq]

CodSpeed Performance Report

Merging #5419 will not alter performance

_{Comparing tartansandal:kjh/use-granian-workers-env-var (b522cf0) with main (c23ffce)}

Summary

✅ 8 untouched benchmarks

[Lendemor]

We've started merging the PRs for 0.8, so we will soon make one that remove the deprecated config props like gunicorn_workers.

So I don't know if we'll take that PR, but we'll make sure that problem is solved in 0.8.

[adhami3310]

superseded by #5422