Fix bytecode ordering dependency in GatewayAutoConfigurationTests

[Kcruz28]

Problem

Found this while running NonDex on the test suite. When running the test suite with certain bytecode reordering patterns,
GatewayAutoConfigurationTests.nettyHttpClientConfigured fails because Spring Boot
cannot resolve metadata for TestEnableWebfluxSecurityAutoConfiguration.

The issue occurs because:

1. The test context auto-discovers all autoconfiguration classes in the classpath
2. Spring Boot's AutoConfigurationSorter tries to read metadata for TestEnableWebfluxSecurityAutoConfiguration
3. Due to bytecode reordering, the class file becomes temporarily inaccessible during classpath scanning
4. This results in a FileNotFoundException that breaks the test

Solution

Use Spring Boot's FilteredClassLoader to explicitly exclude TestEnableWebfluxSecurityAutoConfiguration
from the test's classloader. This prevents Spring Boot from trying to discover and load metadata for
the test-only autoconfiguration, while keeping all other functionality intact.

The change is minimal:

• Adds .withClassLoader(new FilteredClassLoader(...)) to exclude the problematic class
• No changes to test logic or assertions
• No changes to production code

Why This Matters

This type of issue indicates a hidden dependency on bytecode ordering within the test setup.
By fixing it, we:

• Ensure consistent test behavior across different execution environments
• Prevent intermittent CI/CD failures that are hard to debug
• Make the test more robust to future changes in classloading order