Bump version in BWC check after backport

VERSION_HASHED_TOKENS needs to point to 7.2, after #42220 was
merged

Author: jkakavas

x-pack/plugin/security/src/main/java/org/elasticsearch/xpack/security/authc/TokenService.java

@@ -189,7 +189,7 @@ public final class TokenService {
     static final int MINIMUM_BYTES = VERSION_BYTES + TOKEN_LENGTH + 1;
     static final int LEGACY_MINIMUM_BASE64_BYTES = Double.valueOf(Math.ceil((4 * LEGACY_MINIMUM_BYTES) / 3)).intValue();
     static final int MINIMUM_BASE64_BYTES = Double.valueOf(Math.ceil((4 * MINIMUM_BYTES) / 3)).intValue();
-    static final Version VERSION_HASHED_TOKENS = Version.V_8_0_0;
+    static final Version VERSION_HASHED_TOKENS = Version.V_7_2_0;
     static final Version VERSION_TOKENS_INDEX_INTRODUCED = Version.V_7_2_0;
     static final Version VERSION_ACCESS_TOKENS_AS_UUIDS = Version.V_7_2_0;
     static final Version VERSION_MULTIPLE_CONCURRENT_REFRESHES = Version.V_7_2_0;