Add annotations to VTS tests

This helps reviewers understand which VTS requirement these test are
covering

Bug: 302208814
Test: th
Change-Id: I52712d9888b73fc7a9f8eeeb035a3303618efd69

fs_mgr/libsnapshot/partition_cow_creator_test.cpp

@@ -39,6 +39,7 @@ using ::testing::Truly;
 namespace android {
 namespace snapshot {
 
+// @VsrTest = 3.7.6
 class PartitionCowCreatorTest : public ::testing::Test {
   public:
     void SetUp() override {

fs_mgr/libsnapshot/snapshot_test.cpp

@@ -104,6 +104,7 @@ std::string fake_super;
 
 void MountMetadata();
 
+// @VsrTest = 3.7.6
 class SnapshotTest : public ::testing::Test {
   public:
     SnapshotTest() : dm_(DeviceMapper::Instance()) {}

fs_mgr/libsnapshot/vts_ota_config_test.cpp

@@ -21,6 +21,7 @@ static int GetVsrLevel() {
     return android::base::GetIntProperty("ro.vendor.api_level", -1);
 }
 
+// @VsrTest = 3.7.6
 TEST(VAB, Enabled) {
     if (!android::base::GetBoolProperty("ro.build.ab_update", false) && (GetVsrLevel() < __ANDROID_API_T__)) {
         GTEST_SKIP();