Modal and calendar: the calendar is truncated if the modal height is small

[vanessatran-ddi]

The code snippet example taken from
https://deploy-preview-349--abgov-ui-component-docs.netlify.app/components/modal#tab-1#confirm-a-change

(note that this PR 349 is using the latest alpha)

https://github.com/GovAlta/ui-components-docs/pull/349/files#diff-7ae45ad102eab3b6d7e7896acd08c427a9b25b346470d7bc6507b6481575d519R15

As discussed in grooming this issue is likely a result of the removal of the relative property.
#2358

Acceptance Criteria:

• Calendar should be visible fully so we can select first few days

[ArakTaiRoth]

A duplicate of #2655