libsnapshot: Disable 32-bit VTS tests on 64-bit systems.

These tests don't work because 32-bit dependencies are not normally
packaged on a 64-bit system.

Bug: 263062262
Test: builds
Change-Id: I68859a9e9c029a528ee12c02569a3693261c7251
(cherry picked from commit 32fa3e96f4f23256da25fe9115fb3e5011c3299b)
diff --git a/fs_mgr/libsnapshot/Android.bp b/fs_mgr/libsnapshot/Android.bp
index 6db8f13..0d8828a 100644
--- a/fs_mgr/libsnapshot/Android.bp
+++ b/fs_mgr/libsnapshot/Android.bp
@@ -257,6 +257,7 @@
     },
     auto_gen_config: true,
     require_root: true,
+    compile_multilib: "first",
 }
 
 cc_test {