docs: type three boolean docstring parameters as bool, not str

[iridescentWen]

Fixes #14723

What's wrong

Three docstrings annotate a boolean parameter as `str`. Each line contradicts itself, because it
pairs the str type with a boolean default:

File	Line	Parameter	Was	Now
pipelines/pipeline_utils.py	423	silence_dtype_warnings	`str`	bool
modular_pipelines/modular_pipeline.py	2612	silence_dtype_warnings	`str`	bool
pipelines/stable_diffusion/convert_from_ckpt.py	1213	from_safetensors	`str`	bool

str actively misleads: it implies passing "False", which is truthy.

Evidence, from the code rather than the parameter names

silence_dtype_warnings — the same docstring's own signature examples, three lines above the
entry, already write it as a boolean (pipeline_utils.py:408, :410, :412:
to(dtype, silence_dtype_warnings=False)). It is read as
kwargs.pop("silence_dtype_warnings", False) (:431), used as a bare condition (:588
and not silence_dtype_warnings), and internal callers pass True (:1230, :1344). The prose
directly below it reads "Whether to omit warnings…".

from_safetensors — annotated from_safetensors: bool = False at :1156, used as a bare
condition at :1269. The next docstring entry,
load_safety_checker (`bool`, *optional*, defaults to `True`), is the correct spelling of the same
shape.

Validation

$ uvx ruff check <the 3 changed files>
All checks passed!

$ uvx ruff format --check <the 3 changed files>
3 files already formatted

git diff --stat: 3 files, +3/-3.

Self-review (per CONTRIBUTING)

Ran the .ai/skills/self-review rubric against .ai/review-rules.md:

• Blocking issues: none. Docstring text only; no logic, signature, or default changed.
• # Copied from: checked per function, since two of the three fix the same parameter text in
  two files — that is the shape a copy-link usually takes. Both are def to(self, *args, **kwargs)
  (pipeline_utils.py:397, modular_pipeline.py:2586) and neither carries a # Copied from header,
  so editing both by hand is correct rather than fixing one source and running make fix-copies.
  utils/check_copies.py is outside my sparse checkout, so this is the manual equivalent; CI's
  consistency check will confirm.
• Ephemeral context: none added.
• Documentation impact: this is the documentation fix. No docs/ page restates these types.
• Dead code analysis: N/A.

How this was found, and what it deliberately excludes

An AST pass comparing each documented parameter type against its real annotation. It only reports
unambiguous contradictions between two simple types, and skips everything it cannot settle exactly:
unannotated parameters, containers/unions/generics on either side, prose types, and compatible
spellings like bool vs int. After this change it reports 0 for src/diffusers.

Related, deliberately left out — a different problem class that would touch 19 files: 27
docstrings write a boolean default as a quoted string, e.g.
force_zeros_for_empty_prompt (`bool`, *optional*, defaults to `"True"`) in
pipeline_controlnet_sd_xl.py:222 where the signature is bool = True. That is a default-value
formatting issue rather than a wrong type, so it does not belong in the same PR. Happy to follow up
per pipeline family or as one batch — tell me which you prefer.

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🤖 Written with Claude Code. All three sites were read in context and
each type was confirmed against the code that consumes the value.