Add comma for clarity in data-seeding.md

[Copilot]

Adds a missing comma after "relationship" to improve sentence clarity:

• Before: "To add entities that have a relationship the foreign key values need to be specified:"
• After: "To add entities that have a relationship**,** the foreign key values need to be specified:"

Fixes #5317

[Copilot]

Pull request overview

Improves readability in the EF Core documentation by adding a clarifying comma in the “Model managed data” section of the data seeding guide.

Changes:

• Add a missing comma after “relationship” to improve sentence clarity.