CI(macos): silence example-build ld deployment-target warnings in test-distribution

[Fedr]

What

Bump the deployment target of the C/C++ example builds in macos-test (.github/workflows/test-distribution.yml) to 12.7 only on macOS-12 hosts, leaving the SDK default in place everywhere else:

if [ "$(sw_vers -productVersion | cut -d. -f1)" -lt 13 ]; then
  export MACOSX_DEPLOYMENT_TARGET=12.7
fi

Why

The test-distribution / macos-test (x64, macos-12-intel, *x64.pkg) job was producing a wall of linker warnings against every dylib in the installed framework, e.g.:

ld: warning: dylib (.../MeshLib.framework/.../libMeshLibC2.dylib) was built for newer macOS version (12.7) than being linked (12.0)

(See run https://github.com/MeshInspector/MeshLib/actions/runs/26396912525/job/77711295815.)

The mismatch has two ends:

• The framework dylibs are stamped at min-macOS 12.7. MeshLib's top-level CMakeLists.txt (lines 26-28) defaults CMAKE_OSX_DEPLOYMENT_TARGET to 12.7 on macOS, and that value is baked into every libMR*.dylib / libMeshLibC2.dylib shipped in the .pkg.
• The example binaries were stamped at min-macOS 12.0. The cmake .. invocations for examples/cpp-examples and examples/c-examples don't set a deployment target, so AppleClang on the self-hosted macos-12-intel runner falls back to the macOS-12 SDK's default min-macOS of 12.0.

ld then sees a 12.0-target binary linking against 12.7-target dylibs and warns for every example. Only the macos-12-intel cell showed this — on macOS-13+ cells the SDK default min-macOS is already >= 12.7.

Why the fix is conditional

The obvious fix — exporting MACOSX_DEPLOYMENT_TARGET=12.7 unconditionally — fixes macos-12-intel but introduces the symmetric warning on newer cells, because the brew bottles there are built at the host's macOS version:

# macos-13 arm64
ld: warning: dylib (/opt/homebrew/lib/libfmt.12.1.0.dylib) was built for newer macOS version (13.0) than being linked (12.7)
# macos-26 / macos-26-intel
ld: warning: building for macOS-12.7, but linking with dylib '.../libjsoncpp.27.dylib' which was built for newer version 26.0

The warning fires whenever any linked dylib's min-macOS exceeds the binary's link target. Forcing 12.7 everywhere drops the target below the brew bottles on every macOS-13+ host. So the target is bumped to 12.7 only when the host SDK would otherwise default below it (macOS-12); on macOS-13+ the SDK default already covers both MeshLib's 12.7 and the brew bottles.

Scope

CI workflow only. No source, no CMake files, no example logic touched. The 12.7 literal matches the constant in the top-level CMakeLists.txt; if that moves, both should move together.

Test plan / results

Verified on run https://github.com/MeshInspector/MeshLib/actions/runs/26468388117 — all 7 macos-test cells pass with zero ld warnings:

Cell	Original master	Unconditional 12.7	This PR (conditional)
x64, macos-12-intel	65	0	0
x64, macos-15-intel	0	0	0
x64, macos-26-intel	0	133	0
arm64, macos-13	0	124	0
arm64, macos-14	0	0	0
arm64, macos-15	0	0	0
arm64, macos-26	0	133	0

• macos-12-intel cell: original 65 warnings gone.
• All other cells: still warning-free (no regression from the conditional).
• MeshModification example still runs at the end of "Build C++ examples".

Note: test-distribution.yml is invoked via workflow_call from the release pipeline; on this PR it was exercised by applying the upload-binaries label.

[Grantim]

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