Remove redundant list

[martincostello]

Description

Remove allocation for a list that is never used.

Motivation and Context

Noticed while looking at fix for #4445.

Testing

None - trivial change.

Dry-runs

• DotNet Dry-run ID:
  • Pending
  • Completed successfully
  • Failed
• PowerShell Dry-run ID:
  • Pending
  • Completed successfully
  • Failed

Breaking Changes Assessment

N/A

Screenshots (if appropriate)

N/A

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have read the README document
• I have added tests to cover my changes
• All new and existing tests passed

License

• I confirm that this pull request can be released under the Apache 2 license

[martincostello]

Not changed in this PR, but depending on how hot this code path is, it could potentially benefit from the double-lock pattern to avoid acquiring the lock if the cache has a value already:

aws-sdk-net/sdk/src/Core/Amazon.Runtime/AWSRegion.cs

Lines 222 to 227 in 2c44ad4

	public static RegionEndpoint GetRegionEndpoint(bool includeInstanceMetadata)
	{
	lock(_lock)
	{
	if (cachedRegion != null)
	return cachedRegion.Region;

The unconditional lock might explain the performance regression from #4445.

[Copilot]

Pull request overview

Removes an unnecessary allocation in the Core region fallback logic to reduce allocations during region resolution.

Changes:

• Removed an unused List<Exception> allocation in FallbackRegionFactory.GetRegionEndpoint(...).
• Simplified the exception handling path in the region generator loop.

[dscpinheiro]

Started an internal build (DRY_RUN-15ce87e0-644e-413e-ba2e-715c79bb81f6). If it passes we'll merge the PR and it'll be included in the next SDK release.