Update Dockerfile and Rakefile for pico sdk 1.5.0

[yujiyokoo]

This fixes the Docker-based build (docker compose run --rm prk rake) issues I encountered in my environment. I use Docker Desktop 4.11.1 on macOS 12.6.3 M1 Pro. I have not tested it in other environments.

• PICO_SDK_TAG is set to 1.5.0 in Rakefile. Updated in Dockerfile.
• In my environment, pico-sdk version check fails because git status --branch does not seem to return the tag:

# git status --branch
Not currently on any branch.
nothing to commit, working tree clean

but git describe --tags works:

# git describe --tags
1.5.0