Spring SimpleEvaluationContext does not enforce read-only semantics

Backport of gh-33319

Comment From: github-actions[bot]

Fixed via e1ab306506d4e350b119331387f504b726fbc776

Comment From: sbrannen

Reopening to introduce SimpleEvaluationContext.Builder.withAssignmentDisabled().

Comment From: github-actions[bot]

Fixed via 79c7bfdbadb73bdabf5412d477454bdeddb67aa5