Pass int when getting I18n VSA stage summary title

What does this MR do?

Value Stream Analytics summary (top bar) has localized texts with pluralization. This MR makes sure that we always pass an integer value to the localization library (gettext) to get the pluralized text. Passing non-integer values might break the Non-English pluralization rules and cause exceptions.

More context: #220148 (comment 354429839)

• Introduce to_i method for Value objects to get the underlying raw value or 0.
• Add extra test cases for the title.

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

Closes #220148 (closed)