ci: update actions/checkout, setup-python, and cache to current majors

[katsugtgz]

Updates the CI workflows to current GitHub-maintained action versions.

Changes:

• actions/checkout@v2 -> actions/checkout@v7
• actions/setup-python@v2 -> actions/setup-python@v7
• actions/cache@v1/v2 -> actions/cache@v6

Validation:

• YAML parse of all four workflow files passes
• no removed inputs in use (setup-python v7 drops pip-install; these workflows do not use it)
• test matrix keeps Python 3.8 to 3.11, within the versions setup-python v7 still supports

Note: conda.yml, docker.yml, and pypi.yml run on workflow_dispatch only, so those bumps take effect on the next manual run.

Scope: .github/workflows/ only.
Commit author katsugtgz, unsigned.

[katsugtgz]

The workflow runs on this PR are waiting for maintainer approval (first run from this fork). Nothing needed from my side; the checks will start once approved.