Update dependency magic-string to v0.26.2

Editor assessment

A textbook dependency bump: `build: update dependency magic-string to v0.26.2` names the exact package and target version, making the change fully understandable without a diff. The absent body is appropriate — routine version bumps need no rationale, and the rubric exempts small changes from body requirements. The `PR Close #46279` footer is well formed and is the only trailer. Style hygiene is excellent: imperative verb, no trailing period, short subject, no ticket junk, consistent language. Teaching value is inherently limited because there is nothing to explain, but as a clear, correct, self-sufficient message it cleanly satisfies the good anchor.