Stage icu for the macOS osx_arm64 test path too

The stage_icu helper mapped only the Linux uname values, so on the
macOS arm64 test runner uname -m returned "arm64" and the icu
extension was copied to .duckdb/extensions/v1.4.4/arm64 instead of
.../osx_arm64, where DuckDB's autoload looks. The hub fallback is not
reliably resolvable on that runner, so the osx_arm64 Test step failed
to load the extension. Map the OS and architecture to the DuckDB
platform string (linux_amd64, linux_arm64, osx_amd64, osx_arm64) so
the locally built icu is staged at the path autoload expects on every
tested platform; the Linux mapping is unchanged.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: estebanzimanyi

Makefile

@@ -15,16 +15,23 @@ include extension-ci-tools/makefiles/duckdb_extension.Makefile
 # LoadInternal also calls ExtensionHelper::AutoLoadExtension(db, "icu") so
 # the timezone option is honoured. Autoload looks for the extension on disk
 # at $HOME/.duckdb/extensions/<duckdb_version>/<platform>/icu.duckdb_extension
-# and falls back to a hub download. Inside the linux_amd64 test docker
-# container that path is empty and there is no network egress, so the
-# autoload fails. We copy the icu.duckdb_extension that was built locally
-# as part of this extension's build (declared in extension_config.cmake)
-# into the expected path before running the unittester.
+# and falls back to a hub download. That fails both inside the linux_amd64
+# test docker container (empty path, no network egress) and on the macOS
+# osx_arm64 test runner (hub icu not reliably resolvable). We copy the
+# icu.duckdb_extension that was built locally as part of this extension's
+# build (declared in extension_config.cmake) into the expected path,
+# matched to the DuckDB platform string, before running the unittester.
 DUCKDB_VERSION_TAG := v1.4.4
 
 define stage_icu
 	@if [ -f ./build/$(1)/extension/icu/icu.duckdb_extension ]; then \
-	  platform=$$(uname -m | sed 's/x86_64/linux_amd64/;s/aarch64/linux_arm64/'); \
+	  case "$$(uname -s)-$$(uname -m)" in \
+	    Linux-x86_64)  platform=linux_amd64 ;; \
+	    Linux-aarch64) platform=linux_arm64 ;; \
+	    Darwin-arm64)  platform=osx_arm64 ;; \
+	    Darwin-x86_64) platform=osx_amd64 ;; \
+	    *)             platform=$$(uname -m) ;; \
+	  esac; \
 	  target=$$HOME/.duckdb/extensions/$(DUCKDB_VERSION_TAG)/$$platform; \
 	  mkdir -p "$$target" && cp -f ./build/$(1)/extension/icu/icu.duckdb_extension "$$target/" && \
 	  echo "Staged icu.duckdb_extension at $$target/"; \