Reenable Dependabot for internal GitHub actions

[dbanck]

When TSCCR was first introduced, it was not clear that the tool would only update external GitHub actions. This adds the configuration to enable hashicorp/* action updates.

[xiehan]

Jinx, I was just about to submit the same PR. Here's where mine differs slightly from yours.

[dbanck]

GitHub has recently updated the macos-latest runners from amd64 to arm64: https://github.blog/changelog/2024-04-01-macos-14-sonoma-is-generally-available-and-the-latest-macos-runner-image/. Older versions of Terraform aren't available for arm64, hence the failed tests.

It might make sense for this repository to use macos-13 instead.

[bflad]

FYI, in case it helps -- hashicorp/setup-terraform v3.1.0+ will automatically install darwin/amd64 when running on darwin/arm64 for Terraform versions 1.0.2 and earlier which didn't have that release artifact. For example, we still wanted legacy Terraform version coverage with provider acceptance testing on macOS and it seemed like a pragmatic compromise until those legacy Terraform versions are officially deprecated. It'll work as long as Apple/GitHub continue to enable the CPU emulation support.