ci: correct the artifact name in the macOS test jobs

upload-artifact gives an artifact uploaded with "archive: false" the
name of the file, not the name in the "name" input. Download the
tarball by its file name, and find it on disk instead of assuming where
it lands.

.github/workflows/build-macos.yml

@@ -118,10 +118,17 @@ jobs:
       - name: Download TinyGo build
         uses: actions/download-artifact@v8
         with:
-          name: darwin-${{ matrix.goarch }}-double-zipped-${{ steps.version.outputs.version }}
+          # An artifact uploaded with "archive: false" takes the name of the
+          # file, not the name given to upload-artifact. See the comment on
+          # "Collect the release files" in release.yml.
+          name: tinygo${{ steps.version.outputs.version }}.darwin-${{ matrix.goarch }}.tar.gz
           path: build/
+          skip-decompress: true
       - name: Unpack TinyGo build
-        run: tar -xzf build/tinygo${{ steps.version.outputs.version }}.darwin-${{ matrix.goarch }}.tar.gz -C build
+        run: |
+          tarball=$(find build -type f -name 'tinygo*.darwin-*.tar.gz' | head -1)
+          test -n "$tarball"
+          tar -xzf "$tarball" -C build
       - name: Test stdlib packages
         run: make tinygo-test TINYGO=$(PWD)/build/tinygo/bin/tinygo
 
@@ -159,10 +166,17 @@ jobs:
       - name: Download TinyGo build
         uses: actions/download-artifact@v8
         with:
-          name: darwin-${{ matrix.goarch }}-double-zipped-${{ steps.version.outputs.version }}
+          # An artifact uploaded with "archive: false" takes the name of the
+          # file, not the name given to upload-artifact. See the comment on
+          # "Collect the release files" in release.yml.
+          name: tinygo${{ steps.version.outputs.version }}.darwin-${{ matrix.goarch }}.tar.gz
           path: build/
+          skip-decompress: true
       - name: Unpack TinyGo build
-        run: tar -xzf build/tinygo${{ steps.version.outputs.version }}.darwin-${{ matrix.goarch }}.tar.gz -C build
+        run: |
+          tarball=$(find build -type f -name 'tinygo*.darwin-*.tar.gz' | head -1)
+          test -n "$tarball"
+          tar -xzf "$tarball" -C build
       - name: Smoke tests
         run: make ${{ matrix.smoketest }} TINYGO=$(PWD)/build/tinygo/bin/tinygo