Periphery marks `appendInterpolation` as unused.

[rnapier]

Describe the bug StringInterpolation.appendInterpolation methods are being marked unused again. This is the same issue as https://github.com/peripheryapp/periphery/pull/145, but appears to have resurfaced in 3.0.

Reproduction Same as in https://github.com/peripheryapp/periphery/pull/145

Environment Copy the output from running:

3.1.0

swift-driver version: 1.120.5 Apple Swift version 6.1 (swiftlang-6.1.0.110.21 clang-1700.0.13.3)
Target: arm64-apple-macosx15.0

Xcode 16.3
Build version 16E140

[ileitch]

Do you have another reproduction? I'm unable to reproduce using the test case implemented in https://github.com/peripheryapp/periphery/commit/97bdfe17a52d7a3bdb7173939060e963e19ce744