在OracleContainer中，可以使用构建器方法withCopyFileToContainer将init脚本作为SYSDBA运行。
因此，当我使用该方法从 test/resources/sql/initAdditionalSchemas.sql 应用以下init脚本时：

ALTER SESSION SET CONTAINER=XEPDB1;
CREATE USER SCHEMA2 IDENTIFIED BY SCHEMA2PASS QUOTA UNLIMITED ON USERS;
GRANT CREATE SESSION TO SCHEMA2;
GRANT CONNECT, RESOURCE, DBA TO SCHEMA2;

则此测试成功：

@BQTest
@Testcontainers
public class MyTestContainerTest {

    @Container
    static final OracleContainer oracleContainer = new OracleContainer("gvenzl/oracle-xe:21-slim-faststart")
            // no database name, use XEPDB1
            .withUsername("SCHEMA1") // define first schema
            .withPassword("SCHEMA1PASS")
            .withCopyFileToContainer( // define additional schemas
                    MountableFile.forClasspathResource("sql/initAdditionalSchemas.sql"),
                    "/container-entrypoint-initdb.d/initAdditionalSchemas.sql");

    static {
        oracleContainer.start();
    }

    @BQTestTool(BQTestScope.GLOBAL)
    static final DbTester<TcDbTester> testerSchema1 = TcDbTester
            .db(oracleContainer, "SCHEMA1", "SCHEMA1PASS")
            .initDBWithLiquibaseChangelog("classpath:changelogSchema1.yml");

    @BQTestTool(BQTestScope.GLOBAL)
    static final DbTester<TcDbTester> testerSchema2 = TcDbTester
            .db(oracleContainer, "SCHEMA2", "SCHEMA2PASS")
            .initDBWithLiquibaseChangelog("classpath:changelogSchema2.yml");

    @Test
    public void canAccessTablesFromTwoSchemas() {
        Table schema1Table = testerSchema1.getTable("TABLE_FROM_SCHEMA1");
        assertEquals("TABLE_FROM_SCHEMA1", schema1Table.getMetadata().getName().getTable());
        Table schema2Table = testerSchema2.getTable("TABLE_FROM_SCHEMA2");
        assertEquals("TABLE_FROM_SCHEMA2", schema2Table.getMetadata().getName().getTable());
    }
}