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
lock.close();
                } catch (IOException e) {
                    logger.trace(() -> new ParameterizedMessage("failed to release lock [{}]", lock), e);
                }
            }
        }
    }
    private void assertEnvIsLocked() {
        if (closed.get() == false && locks != null) {
            for (Lock lock : locks) {
                try {
                    lock.ensureValid();
                } catch (IOException e) {
                    logger.warn("lock assertion failed", e);
                    throw new IllegalStateException("environment is not locked", e);
                }
            }
        }
    }
    /**
     * This method tries to write an empty file and moves it using an atomic move operation.
     * This method throws an {@link IllegalStateException} if this operation is
     * not supported by the filesystem. This test is executed on each of the data directories.
     * This method cleans up all files even in the case of an error.
     */
    private static void ensureAtomicMoveSupported(final NodePath[] nodePaths) throws IOException {
        for (NodePath nodePath : nodePaths) {
            assert Files.isDirectory(nodePath.path) : nodePath.path + " is not a directory";
            final Path src = nodePath.path.resolve(TEMP_FILE_NAME + ".tmp");
            final Path target = nodePath.path.resolve(TEMP_FILE_NAME + ".final");