Spring SimpleEvaluationContext does not enforce read-only semantics

Backport of gh-33319

Comment From: github-actions[bot]

Fixed via 26f2dad388499faecf99e75b8856788e95d8d658

Comment From: sbrannen

Reopening to introduce SimpleEvaluationContext.Builder.withAssignmentDisabled().

Comment From: github-actions[bot]

Fixed via f9c3d00af07e3b5e634f9161f86a2daacc64d682