This fixes a build failure when attempting to build the main branch using a 6.1 development snapshot toolchain. This failure was introduced by #1069, which added usage of the new @unsafe attribute, and the failure was revealed when we set up the 6.1 CI jobs in #1083.

Here are some relevant related Swift PRs which give context around these changes:

• Introduce @unsafe and the ability to prohibit use of unsafe entities swift#75413
• [SE-0458] Enable unsafe expressions / attributes / for..in effects by default  swift#79645

See the code comment for more details.

Checklist:

• Code and documentation should follow the style of the Style Guide.
• If public symbols are renamed or modified, DocC references should be updated.