chore: Changes from env variable to input in Import GPG key

[oarbusi]

Description

Because of the bump of crazy-max/ghaction-import-gpg from 2.1.0 to 6.1.0, a breaking change has to be fixed for the github action to work. See https://github.com/crazy-max/ghaction-import-gpg for details on how to use it now

This was first changed to gpg-private-key in 3.0.0 https://github.com/crazy-max/ghaction-import-gpg/releases/tag/v3.0.0
Later changed to gpg_private_key in 4.0.0 https://github.com/crazy-max/ghaction-import-gpg/releases/tag/v4.0.0

Link to any related issue(s):

Type of change:

• Bug fix (non-breaking change which fixes an issue). Please, add the "bug" label to the PR.
• New feature (non-breaking change which adds functionality). Please, add the "enhancement" label to the PR.
• Breaking change (fix or feature that would cause existing functionality to not work as expected). Please, add the "breaking change" label to the PR.
• This change requires a documentation update
• Documentation fix/enhancement

Required Checklist:

• I have signed the MongoDB CLA
• I have read the contribution guidelines
• I have checked that this change does not generate any credentials and that they are NOT accidentally logged anywhere.
• I have added tests that prove my fix is effective or that my feature works per HashiCorp requirements
• I have added any necessary documentation (if appropriate)
• I have run make fmt and formatted my code
• If changes include deprecations or removals, I defined an isolated PR with a relevant title as it will be used in the auto-generated changelog.
• If changes include removal or addition of 3rd party GitHub actions, I updated our internal document. Reach out to the APIx Integration slack channel to get access to the internal document.

Further comments

[AgustinBettati]

LGTM. Can you adjust the PR title prefix from fix: to chore: and remove the bug label? This change is not a bug fix for terraform users but instead a fix which is internal to us, so making this adjustment will improve the generated changelog.

[andreaangiolillo]

LGTM