The pricing fetching logic only works for EC2

**Issue:**
When running experiment on Bedrock, the uploaded pricing.yml file is not picked up. The function always goes to the pricing_fallback.yml file.

**Details:**

The pricing function [link](https://github.com/aws-samples/foundation-model-benchmarking-tool/blob/main/src/fmbench/scripts/pricing.py) is designed for EC2. When running Bedrock experiments, after checking [EC2 price](https://github.com/aws-samples/foundation-model-benchmarking-tool/blob/main/src/fmbench/scripts/pricing.py#L142), the logic goes straight to the pricing_fallback.yml, instead of pricing.yml.