libsnapshot: Disable the update space swap test on non-VABC.

// Test that shrinking and growing partitions at the same time is handled

// correctly in VABC.

TEST_F(SnapshotUpdateTest, SpaceSwapUpdate) {

    if (!IsCompressionEnabled()) {

        // b/179111359

        GTEST_SKIP() << "Skipping Virtual A/B Compression test";

    }

    // OTA client blindly unmaps all partitions that are possibly mapped.

    for (const auto& name : {"sys_b", "vnd_b", "prd_b"}) {

        ASSERT_TRUE(sm->UnmapUpdateSnapshot(name));