[vcpkg-scripts] Exclude .a files from patchelf

[LandryNorris]

Exclude static libraries (.a) files from patchelf checks. This prevents systems that only build static libraries from requiring patchelf to be installed. Since a static library is not a valid ELF file, patchelf will fail when run on it anyways.

Fixes #40032

[LandryNorris]

Given that CMake allows a dev to set the CMAKE_EXECUTABLE_SUFFIX, would it be good to use CMake's file(READ <filename> <variable> [OFFSET <offset>] [LIMIT <max-in>] [HEX]) call to check for an ELF header instead of relying on known extensions to exclude? This would add a more authoritative check that would only require patchelf to be installed and run if the file truly is an ELF. If this is a desired change, I could create a PR.

[Osyotr]

Skipping files based on extension is much cheaper than reading them.

[data-queue]

/azp run

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