fix(openjdk/v8): linux-only until darwin boot-JDK extraction sorted

configure rejects the extracted Temurin 8 darwin tarball as "not a
valid Boot JDK" even with --strip-components=4. The macOS Temurin
tarball is a nested Contents/Home/ structure and our path flattening
isn't getting bin/java to land where configure looks.

Restrict to linux until the darwin-specific extraction path is
worked out (same temporary measure as R pkgxdev#13045, octave pkgxdev#13054).

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

Author: tannevaled

projects/openjdk.org/v8/package.yml

@@ -28,10 +28,12 @@ versions:
     }
 
 platforms:
+  # darwin Temurin tarball layout (Contents/Home/) defeats our
+  # --strip-components=4 path-flattening: configure still rejects
+  # the result as "not a valid Boot JDK". Needs darwin-specific
+  # extraction logic we haven't worked out yet; restrict to linux.
   - linux/x86-64
   - linux/aarch64
-  - darwin/x86-64
-  - darwin/aarch64
 
 dependencies:
   freetype.org: '*'