Address env var default mismatch

[taiidani]

What Is Changing

Fixing an issue causing failures when specifying pure env vars for the new provider framework. The prepared configuration between both providers must match, and the SDK using DefaultFunc to provide default env vars triggers a mismatch.

Updating the SDK implementation to match the Framework implementation to address these errors.

See https://discuss.hashicorp.com/t/muxing-upgraded-tfsdk-and-framework-provider-with-default-provider-configuration/43945/7 for more context.

Test Steps

• [x] Have you updated the docs/ folder to match your change?
• [x] Have you exercised your change using the examples/ docker compose setup?

make testacc