Preserve `tested-with` formatting from existing `.cabal` file

[webdevred]

Problem:
hpack changes capitalization and spacing in the tested-with section, breaking Gild formatting. Related: #617

Expected behavior:
Maintain exact formatting, including capitalization, spacing, and commas.

Example:

-- Before (Gild-formatted)

tested-with:
  ghc ==9.4.7
  ghc ==9.6.6

-- After (hpack)

tested-with:
  GHC == 9.4.7,
  GHC == 9.6.6

[sol]

If commas are optional, then that is something we want to address. Again I will need to know:

1. Starting from which cabal-version is the comma optional?

The other things are less clear cut, as they are not strictly better.

What is the original package.yaml that produces this output (minimal example).

[webdevred]

Hello, Sorry for the late update, there has been a lot happening during the latest weeks. I created a example repo for demonstrating how cabal gild formats files which were created by hpack.

Hpack example formatted by cabal gild: https://github.com/webdevred/hpack-example/commit/bf5f10b661618f08c24d4b1f33f7d94c5b77f2e4#diff-82b199226141b11408adea375e7906f2b46cb334c109d99525adcf6cc95712f3R114

Regarding this issue, I found this in the Cabal source code. https://github.com/haskell/cabal/blob/ae2ea9ecdb01e67d9f4801080be3d56cb4525422/Cabal-syntax/src/Distribution/Parsec.hs#L362

Best regards, webdevred