Replace v-html with v-safe-html in parallel_diff_table_row.vue

What does this MR do?

This MR replaces v-html with v-safe-html in app/assets/javascripts/diffs/components/parallel_diff_table_row.vue.

This relates to #241963 (closed).

Steps to test

1. Create/go to a merge request with changes
2. Open the diff and set "compare changes" to "side-by-side" using the cog dropdown at the top right
3. Check that the diff is shown correctly.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team