Fix: Anthropic LLM merge consecutive messages with same role (#12013)

...-index-llms-anthropic/llama_index/llms/anthropic/utils.py

...tegrations/llms/llama-index-llms-anthropic/pyproject.toml

...integrations/llms/llama-index-llms-bedrock/pyproject.toml

...tions/llms/llama-index-llms-bedrock/tests/test_bedrock.py