increase MACOSX_DEPLOYMENT_TARGET, but only for libabseil-tests

Otherwise, the build fails with:
```
absl/functional/internal/any_invocable.h:624:28: error: aligned allocation function of type 'void *(std::size_t, std::align_val_t)' is only available on macOS 10.13 or newer
    state_.remote.target = ::new T(std::forward<Args>(args)...);
                           ^
```

recipe/build-abseil.sh

@@ -13,6 +13,12 @@ fi
 if [[ "$PKG_NAME" == "libabseil-tests" ]]; then
     CMAKE_ARGS="${CMAKE_ARGS} -DBUILD_TESTING=ON -DABSL_BUILD_TESTING=ON"
     CMAKE_ARGS="${CMAKE_ARGS} -DABSL_USE_EXTERNAL_GOOGLETEST=ON -DABSL_FIND_GOOGLETEST=ON"
+    if [[ "${target_platform}" == osx-* ]]; then
+        # test targets require C11's aligned_alloc, which doesn't compile even
+        # with a newer MACOSX_SDK_VERSION; need to bump target version too
+        CMAKE_ARGS="$(echo $CMAKE_ARGS | sed 's/-DCMAKE_OSX_DEPLOYMENT_TARGET=10.9 //g')"
+        CMAKE_ARGS="${CMAKE_ARGS} -DCMAKE_OSX_DEPLOYMENT_TARGET=10.13"
+    fi
 fi
 
 cmake -G Ninja \

recipe/meta.yaml

@@ -147,6 +147,9 @@ outputs:
       run:
         - gtest
         - {{ pin_subpackage("libabseil", exact=True) }}
+      run_constrained:
+        # only for libabseil-tests, see build-abseil.sh
+        - __osx >=10.13  # [osx and x86_64]
 
     test:
       requires: