Bump serialize-javascript and @x-govuk/nhsuk-eleventy-plugin

Bumps [serialize-javascript](https://github.com/yahoo/serialize-javascript) to 7.0.5 and updates ancestor dependency [@x-govuk/nhsuk-eleventy-plugin](https://github.com/x-govuk/nhsuk-eleventy-plugin). These dependencies need to be updated together.


Updates `serialize-javascript` from 6.0.2 to 7.0.5
- [Release notes](https://github.com/yahoo/serialize-javascript/releases)
- [Commits](yahoo/serialize-javascript@v6.0.2...v7.0.5)

Updates `@x-govuk/nhsuk-eleventy-plugin` from 1.1.1 to 1.2.0
- [Release notes](https://github.com/x-govuk/nhsuk-eleventy-plugin/releases)
- [Commits](x-govuk/nhsuk-eleventy-plugin@v1.1.1...v1.2.0)

---
updated-dependencies:
- dependency-name: serialize-javascript
  dependency-version: 7.0.5
  dependency-type: indirect
- dependency-name: "@x-govuk/nhsuk-eleventy-plugin"
  dependency-version: 1.2.0
  dependency-type: direct:production
...

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Author: dependabot[bot]