Align sass version pin with ecosystem

[alanorth]

Description

Use "^" instead of "~" to match dependabot's behavior, which bumps minor and patch releases. This is also closer to the behavior of sass-loader, which we use and also depends on sass.

See: https://github.com/DSpace/dspace-angular/blob/main/.github/dependabot.yml#L73-L80
See: https://github.com/webpack/sass-loader/blob/v12.6.0/package.json

Note: next we should evaluate moving to a newer version of sass-loader, as ours is 4 years old, as well as migrating to sass-embedded, which is the recommended implementation of sass as of 2024. This can also result in massive performance increases.

Instructions for Reviewers

Please add a more detailed description of the changes made by your PR. At a minimum, providing a bulleted list of changes in your PR is helpful to reviewers.

List of changes in this PR:

• Update sass version pin in package.json

Include guidance for how to test or review your PR.

To test this PR you should run npm install and then npm run start:prod and make sure the build works without any new errors or warnings, and that the site's style looks OK.

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[tdonohue]

👍 Thanks @alanorth ! This looks good to me too