Allow libyaml-linked PyYAML wheel in Linux onedir builds

[dwoz]

What does this PR do?

Adds pyyaml to the --only-binary allow-list for Linux onedir builds so pip installs PyYAML's manylinux2014 wheel (which bundles libyaml) instead of source-building it under the relenv toolchain.

Why

The Linux onedir build passes --no-binary=:all: to pip so every runtime dependency is compiled against the relenv toolchain. PyYAML's setup.py autodetects libyaml at compile time; because the relenv toolchain does not build or ship libyaml, the source build silently falls back to a pure-Python parser and the resulting onedir has no yaml.CSafeLoader and no _yaml*.so extension.

Salt's yamlloader uses getattr(yaml, "CSafeLoader", yaml.SafeLoader) so it does not crash, but every YAML load (configs, pillars, states, returners, mine, event bus) runs through the pure-Python parser, which is 10-20x slower. Users with segmented configs (many small pillar/state files) have reported salt-run salt.cmd test.ping taking ~20s where a libyaml-linked build completes in well under a second.

Reproduction

On any current 3006.27 or 3008.1 onedir install:

/opt/saltstack/salt/bin/python3 -c "import yaml; print(hasattr(yaml, 'CSafeLoader'))"
False

The reporter's workaround is:

/opt/saltstack/salt/bin/python3 -m pip install --force-reinstall --no-deps --only-binary :all: PyYAML==6.0.3

which pulls the manylinux wheel and restores CSafeLoader. This PR does the equivalent at build time so users get a libyaml-linked PyYAML out of the box.

Scope

Linux only. The Windows path does not use --no-binary=:all:, so pip already prefers the win_amd64 wheel (which bundles libyaml). macOS is unaffected for the same reason.

Licensing

LibYAML is MIT-licensed, matching PyYAML itself; bundling it via the manylinux wheel introduces no new license obligations. This mirrors the existing precedent for maturin, cassandra-driver, hatchling, cmake, ninja, and protobuf in the same allow-list.

Test plan

• Reproduced on current 3008.1 onedir: hasattr(yaml, 'CSafeLoader') == False
• Verified PyYAML 6.0.3 publishes cp3.10 through cp3.14 manylinux2014_x86_64 wheels
• Build Source Packages CI must pass on this branch to confirm pip accepts the new allow-list entry and produces an onedir with _yaml*.so

Fixes #69907

[dwoz]

3006.x backport: #69950