SparkSessionCatalog with JDBC catalog: SHOW TABLES IN ... returns error but table exists in JDBC catalog

### Apache Iceberg version

1.5.0 (latest release)

### Query engine

Spark

### Please describe the bug 🐞

# The issue

Issue with SparkSessionCatalog when using it with a non-Hive catalog

## Repro

My expectations are based on the [documentation](https://iceberg.apache.org/docs/1.5.0/spark-configuration/#catalog-configuration):

```
org.apache.iceberg.spark.SparkSessionCatalog adds support for Iceberg tables to Spark's built-in catalog, and delegates to the built-in catalog for non-Iceberg tables
```

Note that `spark_catalog` is a `org.apache.iceberg.spark.SparkSessionCatalog`

### Test Set 1:

NOTE: `spark.sql.defaultCatalog = spark_catalog`

```
CREATE
OR replace TABLE test_schema.iceberg_table USING iceberg partitioned BY (DAY (ts), truncate (2, id)) AS
SELECT
1 AS id,
TIMESTAMP('2000-01-01 01') AS ts,
'a' AS col1
```

```
show tables in test_schema
```

Expected: the table
Actual: ❌ `org.apache.spark.sql.catalyst.analysis.NoSuchDatabaseException: [SCHEMA_NOT_FOUND] The schema 'test_schema' cannot be found. Verify the spelling and correctness of the schema and catalog.`

```
show tables in spark_catalog.test_schema
```

Expected: the table
Actual: ❌ `org.apache.spark.sql.catalyst.analysis.NoSuchDatabaseException: [SCHEMA_NOT_FOUND] The schema 'test_schema' cannot be found. Verify the spelling and correctness of the schema and catalog.`

```
show tables in iceberg_catalog.test_schema
```

Expected: the table
Actual: ❌ `org.apache.iceberg.exceptions.NoSuchNamespaceException: Namespace does not exist: test_schema`

```
select * from test_schema.iceberg_table
```

Expected: the table content
Actual: ✅ the table content

```
select * from spark_catalog.test_schema.iceberg_table
```

Expected: the table content
Actual: ✅ the table content

```
select * from iceberg_catalog.test_schema.iceberg_table
```

Expected: the table content
Actual: ❌ `org.apache.hive.service.cli.HiveSQLException: Error running query: [TABLE_OR_VIEW_NOT_FOUND]`

### Test Set 2:

I've tried setting the default catalog: `spark.sql.defaultCatalog = iceberg_catalog`

```
CREATE
OR replace TABLE test_schema.iceberg_table USING iceberg partitioned BY (DAY (ts), truncate (2, id)) AS
SELECT
1 AS id,
TIMESTAMP('2000-01-01 01') AS ts,
'a' AS col1
```

The result:

```
show tables in test_schema
```

Expected: the table
Actual: ✅ the table

```
show tables in spark_catalog.test_schema
```

Expected: the table
Actual: ❌ `org.apache.spark.sql.catalyst.analysis.NoSuchDatabaseException: [SCHEMA_NOT_FOUND] The schema 'test_schema' cannot be found. Verify the spelling and correctness of the schema and catalog.`

```
show tables in iceberg_catalog.test_schema
```

Expected: the table
Actual: ✅ the table

```
select * from test_schema.iceberg_table
```

Expected: the table content
Actual: ✅ the table content

```
select * from spark_catalog.test_schema.iceberg_table
```

Expected: the table content
Actual: ❌ `org.apache.spark.sql.AnalysisException: [TABLE_OR_VIEW_NOT_FOUND] The table or view 'spark_catalog'.'test_schema'.'iceberg_table' cannot be found.`

```
select * from iceberg_catalog.test_schema.iceberg_table
```

Expected: the table content
Actual: ✅ the table content

# The Setup:

iceberg : 1.5.0
Java Version : 11.0.22 (Eclipse Adoptium)
Scala Version : version 2.12.18 (offical image with little tweaks)

| Config | value |
| --- | --- |
|spark.sql.catalog.iceberg_catalog | org.apache.iceberg.spark.SparkCatalog|
|spark.sql.catalog.iceberg_catalog.io-impl | org.apache.iceberg.gcp.gcs.GCSFileIO|
|spark.sql.catalog.iceberg_catalog.jdbc.password | *********(redacted)|
|spark.sql.catalog.iceberg_catalog.jdbc.schema-version | V1|
|spark.sql.catalog.iceberg_catalog.jdbc.useSSL | false|
|spark.sql.catalog.iceberg_catalog.jdbc.user | *********(redacted)|
|spark.sql.catalog.iceberg_catalog.jdbc.verifyServerCertificate | false|
|spark.sql.catalog.iceberg_catalog.table-default.write.metadata.delete-after-commit.enabled | true|
|spark.sql.catalog.iceberg_catalog.table-default.write.metadata.previous-versions-max | 50|
|spark.sql.catalog.iceberg_catalog.type | jdbc|
|spark.sql.catalog.iceberg_catalog.uri | jdbc:postgresql://localhost:5432/iceberg-catalog|
|spark.sql.catalog.iceberg_catalog.warehouse | gs://spark_warehouse_staging|
|spark.sql.catalog.spark_catalog | org.apache.iceberg.spark.SparkSessionCatalog|
|spark.sql.catalog.spark_catalog.io-impl | org.apache.iceberg.gcp.gcs.GCSFileIO|
|spark.sql.catalog.spark_catalog.jdbc.password | *********(redacted)|
|spark.sql.catalog.spark_catalog.jdbc.schema-version | V1|
|spark.sql.catalog.spark_catalog.jdbc.useSSL | false|
|spark.sql.catalog.spark_catalog.jdbc.user | *********(redacted)|
|spark.sql.catalog.spark_catalog.jdbc.verifyServerCertificate | false|
|spark.sql.catalog.spark_catalog.type | jdbc|
|spark.sql.catalog.spark_catalog.uri | jdbc:postgresql://localhost:5432/iceberg-catalog|
|spark.sql.catalog.spark_catalog.warehouse | gs://spark_warehouse_staging|
|spark.sql.catalogImplementation | hive|
|spark.sql.defaultCatalog | spark_catalog|
|spark.sql.extensions | org.apache.sedona.sql.SedonaSqlExtensions,org.apache.iceberg.spark.extensions.IcebergSparkSessionExtensions|

Start by reading org.apache.iceberg.spark.SparkSessionCatalog and SparkCatalog, then reproduce the SHOW TABLES and SELECT queries using the listed JDBC and catalog settings. Done means the catalog consistently resolves the existing JDBC-backed namespace and table for the demonstrated qualified and unqualified queries, without the reported schema or table-not-found errors.

Written by the indexing model from the issue text.