deps(instrumentation): Move `@types/shimmer` into `devDependencies`

[lforst]

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Which problem is this PR solving?

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Fixes https://github.com/getsentry/sentry-javascript/issues/12682

Short description of the changes

Shimmer has a harmful type definition (https://github.com/DefinitelyTyped/DefinitelyTyped/pull/69966) which conflicts with typings in certain situations (https://github.com/getsentry/sentry-javascript/issues/12682) but in general, typings should not end up in the normal dependencies.

Type of change

Please delete options that are not relevant.

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

How Has This Been Tested?

No tests necessary I think.

Checklist:

• [x] Followed the style guidelines of this project
• [ ] ~Unit tests have been added~
• [ ] ~Documentation has been updated~