During upgrades from 7.x to 8.x if a node was holding a frozen cache file, the system considers that as an unknown file and prevents starting the node:
```
java.lang.IllegalStateException: unexpected file/folder encountered during data folder upgrade: /app/data/nodes/0/shared_snapshot_cache
	at org.elasticsearch.env.NodeEnvironment.upgradeLegacyNodeFolders(NodeEnvironment.java:443) ~[elasticsearch-8.0.1.jar:8.0.1]
	at org.elasticsearch.env.NodeEnvironment.<init>(NodeEnvironment.java:290) ~[elasticsearch-8.0.1.jar:8.0.1]
	at org.elasticsearch.node.Node.<init>(Node.java:388) ~[elasticsearch-8.0.1.jar:8.0.1]
	at org.elasticsearch.node.Node.<init>(Node.java:277) ~[elasticsearch-8.0.1.jar:8.0.1]
	at org.elasticsearch.bootstrap.Bootstrap$5.<init>(Bootstrap.java:234) ~[elasticsearch-8.0.1.jar:8.0.1]
	at org.elasticsearch.bootstrap.Bootstrap.setup(Bootstrap.java:234) ~[elasticsearch-8.0.1.jar:8.0.1]
	at org.elasticsearch.bootstrap.Bootstrap.init(Bootstrap.java:358) [elasticsearch-8.0.1.jar:8.0.1]
	at org.elasticsearch.bootstrap.Elasticsearch.init(Elasticsearch.java:166) [elasticsearch-8.0.1.jar:8.0.1]
	at org.elasticsearch.bootstrap.Elasticsearch.execute(Elasticsearch.java:157) [elasticsearch-8.0.1.jar:8.0.1]
	at org.elasticsearch.cli.EnvironmentAwareCommand.execute(EnvironmentAwareCommand.java:77) [elasticsearch-8.0.1.jar:8.0.1]
	at org.elasticsearch.cli.Command.mainWithoutErrorHandling(Command.java:112) [elasticsearch-cli-8.0.1.jar:8.0.1]
	at org.elasticsearch.cli.Command.main(Command.java:77) [elasticsearch-cli-8.0.1.jar:8.0.1]
	at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:122) [elasticsearch-8.0.1.jar:8.0.1]
	at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:80) [elasticsearch-8.0.1.jar:8.0.1]
```
These files are expected files and should be ignored/accepted during the data folder upgrade.
server/src/main/java/org/elasticsearch/env/NodeEnvironment.java
IOUtils.fsync(legacyNodesPath, false);
                    IOUtils.fsync(dataPath, true);
                }
            }
            if (DiscoveryNode.canContainData(settings) == false) {
                if (DiscoveryNode.isMasterNode(settings) == false) {
                    ensureNoIndexMetadata(nodePaths);
                }
                ensureNoShardData(nodePaths);
            }
            this.nodeMetadata = loadNodeMetadata(settings, logger, nodePaths);
            success = true;
        } finally {
            if (success == false) {
                close();
            }
        }
    }
    /**
     * Upgrades all data paths that have been written to by an older ES version to the 8.0+ compatible folder layout,
     * removing the "nodes/${lockId}" folder prefix
     */
    private static boolean upgradeLegacyNodeFolders(Logger logger, Settings settings, Environment environment, NodeLock nodeLock)
        throws IOException {
        boolean upgradeNeeded = false;
        
        for (Path path : environment.dataFiles()) {
            final Path nodesFolderPath = path.resolve("nodes");
            if (Files.isDirectory(nodesFolderPath)) {
                final List<Integer> nodeLockIds = new ArrayList<>();