Incorrect substitution of a variable for a blank node in a service pattern

### Version

5.3.0

### What happened?

During my experiments, I observed that Jena incorrectly evaluates the following federated query, which uses a blank node:

```sparql
PREFIX sd:

SELECT * WHERE {
BIND(bnode() as ?BN)

SERVICE {
?S sd:endpoint ?BN.
}
}
```

This query should not return any solutions because blank nodes are only locally scoped within RDF stores. However, it returns the following result:

| ?BN | ?S |
|-|-|
| _:b0 | <https://idsm.elixir-czech.cz/sparql/endpoint/idsm> |

The problem arises because Jena inappropriately substitutes `?BN` with `_:b0` when it evaluates the service pattern:

```sparql
SELECT *
WHERE
{ ?S _:b0 }
```

### Relevant output and stacktrace

```shell

```

### Are you interested in making a pull request?

None

No source file or test is identified in the report. Start by reproducing the federated SPARQL query on Jena 5.3.0 and trace service-pattern evaluation where the blank node is substituted; done means the query returns no solutions because the blank node remains locally scoped.

Written by the indexing model from the issue text.