Conditional annotations are always included in `STRING` annotations

Bug report

Bug description:

If an annotation is excluded via a conditional block it is correctly excluded in VALUE and FORWARDREF annotations but is incorrectly included under STRING annotations.

from annotationlib import get_annotations, Format

class Example:
    a: int
    if False:
        b: str

print(get_annotations(Example))
print(get_annotations(Example, format=Format.STRING))

{'a': <class 'int'>}
{'a': 'int', 'b': 'str'}

'b' should not be included in string annotations here.

CPython versions tested on:

3.14, 3.15, CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-156516

Reproduce the example with get_annotations and Format.STRING first, then inspect the annotationlib implementation and its relevant tests. Done means conditional annotations such as b are absent from STRING results, matching VALUE and FORWARDREF behavior, with the regression covered by passing tests.