CI Yaml: use anchors to dedupe, and latest actions, add HDF5 2.1.1

[scivision]

• Use Yaml anchors to greatly deduplicate specifications
• use latest GitHub Actions
• add HDF5 2.1.1 as a CMake test case

[Copilot]

Pull request overview

This PR updates the GitHub Actions CI workflows to reduce duplication via YAML anchors, refresh action versions, and expand the Linux CMake test matrix to cover HDF5 2.1.1.

Changes:

• Introduce YAML anchors/aliases to deduplicate repeated checkout and HDF5 cache steps across jobs.
• Update workflow runner/action versions (e.g., macOS runner label; actions/checkout, actions/cache).
• Add HDF5 2.1.1 to the Linux CMake matrix.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
.github/workflows/run_tests_macos.yml	Switches macOS runner label and adds anchors for checkout/cache reuse across jobs.
.github/workflows/run_tests_linux.yml	Adds anchors for checkout/cache reuse, updates cache action version, and expands HDF5 matrix to include 2.1.1.
.github/workflows/run_tests_docker.yml	Cleans up YAML formatting and deduplicates checkout step via an anchor.

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