test: retry transient share-manager migration errors

[fredrikblau]

Description

The acceptance HTTP helper now retries the specific transient 500 response emitted while the share manager is migrating. Other 500 responses remain non-retryable.

Related Issue

Fixes #3387

Motivation and Context

The share manager intentionally rejects writes during migration with share manager is currently migrating, please retry. Acceptance setup can hit this window while creating a space, causing a flaky test failure.

Issue verification

Verified against the failure recorded in issue #3387: the acceptance test receives HTTP 500 while the share manager is migrating. The current vendored backend path confirms that this exact message is intentionally returned during migration. A live acceptance reproduction was not run because PHP and Composer are unavailable in the environment.

How Has This Been Tested?

• git diff --check
• Inspected the current backend migration guard and acceptance request flow.
• PHP lint/style checks could not run because PHP and Composer are unavailable.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Tests only (no production source changes)

Checklist

• Code changes
• Unit tests added
• Acceptance tests added
• Documentation added

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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