BBD: content_hash encounters plaintext when updating senstive input

[grubmeshi]

See this error encountered while upgrading the Github Connector BBD (see meshstack-hub) for trial-cloudfoundation:

11:41:43.255 STDOUT tofu: meshstack_building_block_definition.aks_github_connector: Modifying...
11:41:43.356 STDERR tofu: ╷
11:41:43.356 STDERR tofu: │ Error: Failed to determine content hash
11:41:43.356 STDERR tofu: │
11:41:43.356 STDERR tofu: │   with meshstack_building_block_definition.aks_github_connector,
11:41:43.357 STDERR tofu: │   on meshstack_integration.tf line 56, in resource "meshstack_building_block_definition" "aks_github_connector":
11:41:43.357 STDERR tofu: │   56: resource "meshstack_building_block_definition" "aks_github_connector" {
11:41:43.357 STDERR tofu: │
11:41:43.357 STDERR tofu: │ Content hashing of version_spec as client DTO failed: key path
11:41:43.357 STDERR tofu: │ *[inputs]*[GITHUB_APP_PEM_FILE]*[argument][plaintext] matches one of
11:41:43.357 STDERR tofu: │ disallowed keys [plaintext buildingBlockDefinitionRef]
11:41:43.357 STDERR tofu: ╵
11:41:43.427 ERROR  error occurred:

* Failed to execute "tofu apply" in ./.terragrunt-cache/4Bwh86AE3q24o8D66kwq3M0wthU/iSx1lOB6E4BzUFMTYqngunlVpW4/modules/aks/github-connector
  ╷
  │ Error: Failed to determine content hash
  │
  │   with meshstack_building_block_definition.aks_github_connector,
  │   on meshstack_integration.tf line 56, in resource "meshstack_building_block_definition" "aks_github_connector":
  │   56: resource "meshstack_building_block_definition" "aks_github_connector" {
  │
  │ Content hashing of version_spec as client DTO failed: key path
  │ *[inputs]*[GITHUB_APP_PEM_FILE]*[argument][plaintext] matches one of
  │ disallowed keys [plaintext buildingBlockDefinitionRef]
  ╵

  exit status 1