[BUG] On new Homebrew 6 calling postflight is deprecated

[back-2-95]

Describe the bug

On new Homebrew 6 calling postflight is deprecated.

To Reproduce
Steps to reproduce the behavior. Please include output from running the command with --debug.

1. Update Homebrew to latest version 6.x.x
2. Install Doppler using Homebrew
3. See error

Expected behavior

No deprecation warning.

Desktop (please complete the following information):

• OS: macOS Golden Gate
• Version 27.0

CLI Version:
Version: at least 3.76.5 and 3.76.6

Additional context
This is what Homebrew shows:

Warning: Calling postflight is deprecated! Use postflight_steps instead.
Please report this issue to the dopplerhq/homebrew-cli tap (not Homebrew/* repositories), or even better, submit a PR to fix it:
/opt/homebrew/Library/Taps/dopplerhq/homebrew-cli/Casks/doppler.rb:39

[jbdoyon-enoda]

Related/previous work on this: #557
and on the actual, generated homebrew repo:
DopplerHQ/homebrew-doppler#3

Based on my reading, I expect the cli-side code to generate the homebrew code, so the first link may be the proper fix.

I don't know why any of those PRs were closed by the author with no discussion by others, these do look worth pushing for to fix the deprecation warning.