Properly test Id::retain_autoreleased

Author: madsmtm

.github/workflows/apple.yml

@@ -77,3 +77,9 @@ jobs:
         command: test
         # Not using --all-features because some features are nightly-only
         args: --verbose --no-fail-fast --features block,exception,catch_all,verify_message
+
+    - name: Test objc_retainAutoreleasedReturnValue
+      uses: actions-rs/cargo@v1
+      with:
+        command: test
+        args: --package objc2-foundation --test objc_id_retain_autoreleased --release

.github/workflows/gnustep.yml

@@ -115,3 +115,9 @@ jobs:
         command: test
         # Not using --all-features because some features are nightly-only
         args: --verbose --no-fail-fast --features gnustep-1-9,block,exception,catch_all,verify_message
+
+    - name: Test objc_retainAutoreleasedReturnValue
+      uses: actions-rs/cargo@v1
+      with:
+        command: test
+        args: --package objc2-foundation --test objc_id_retain_autoreleased --release

objc2-foundation/tests/objc_id_retain_autoreleased.rs

@@ -25,6 +25,11 @@ fn create_data(bytes: &[u8]) -> Id<NSData, Shared> {
 
 #[test]
 fn test_retain_autoreleased() {
+    #[cfg(gnustep)]
+    unsafe {
+        objc2::__gnustep_hack::get_class_to_force_linkage()
+    };
+
     autoreleasepool(|_| {
         let data = create_data(b"12");
         // The autorelease-return-mechanism has to "warm up" somehow? At least