[Bug]: Replace yaml.safe_load after update to ruamel.yaml

[rly]

What happened?

ruamel.yaml.safe_load was deprecated years ago and finally removed in the latest version of ruamel.yaml. Running validate_hdmf_spec with that version installed causes an error.

Steps to Reproduce

Download nwb-schema repo from https://github.com/NeurodataWithoutBorders/nwb-schema
and run `validate_hdmf_spec core -m nwb.schema.json`

Traceback

Run validate_hdmf_spec core -m nwb.schema.json
  validate_hdmf_spec core -m nwb.schema.json
  shell: /usr/bin/bash -e {0}
  env:
    pythonLocation: /opt/hostedtoolcache/Python/3.12.0/x64
    PKG_CONFIG_PATH: /opt/hostedtoolcache/Python/3.12.0/x64/lib/pkgconfig
    Python_ROOT_DIR: /opt/hostedtoolcache/Python/3.12.0/x64
    Python2_ROOT_DIR: /opt/hostedtoolcache/Python/3.12.0/x64
    Python3_ROOT_DIR: /opt/hostedtoolcache/Python/3.12.0/x64
    LD_LIBRARY_PATH: /opt/hostedtoolcache/Python/3.12.0/x64/lib
Traceback (most recent call last):
  File "/opt/hostedtoolcache/Python/3.12.0/x64/bin/validate_hdmf_spec", line 8, in <module>
    sys.exit(main())
             ^^^^^^
  File "/opt/hostedtoolcache/Python/3.12.0/x64/lib/python3.12/site-packages/hdmf/testing/validate_spec.py", line 52, in main
    validate_spec(ipath, args.metaschema)
  File "/opt/hostedtoolcache/Python/3.12.0/x64/lib/python3.12/site-packages/hdmf/testing/validate_spec.py", line 35, in validate_spec
    instance = yaml.safe_load(f_nwb)
               ^^^^^^^^^^^^^^^^^^^^^
  File "/opt/hostedtoolcache/Python/3.12.0/x64/lib/python3.12/site-packages/ruamel/yaml/main.py", line 1105, in safe_load
    error_deprecation('safe_load', 'load', arg="typ='safe', pure=True")
  File "/opt/hostedtoolcache/Python/3.12.0/x64/lib/python3.12/site-packages/ruamel/yaml/main.py", line 1039, in error_deprecation
    raise AttributeError(s, name=None)
AttributeError: 
"safe_load()" has been removed, use

  yaml = YAML(typ='safe', pure=True)
  yaml.load(...)

instead of file "/opt/hostedtoolcache/Python/3.12.0/x64/lib/python3.12/site-packages/hdmf/testing/validate_spec.py", line 35

    instance = yaml.safe_load(f_nwb)

### Operating System

macOS

### Python Executable

Conda

### Python Version

3.12

### Package Versions

_No response_