Improve Media Card block stability through transforms testing

[AnthonyLedesma]

New Transforms tests for Media Card block.

Test changes using

npx jest --config .dev/tests/jest/jest.config.js ./src/blocks/media-card/test/transforms.spec.js

 PASS  src/blocks/media-card/test/transforms.spec.js
  coblocks/media-card transforms
    ✓ should transform from core/image block (2ms)
    ✓ should transform from core/video block (1ms)
    ✓ should transform from core/media-text block (1ms)
    ✓ should transform to core/image block
    ✓ should transform to core/video block (1ms)
    ✓ should transform to core/media-text block (2ms)
    ✓ should transform when :card prefix is seen

Test Suites: 1 passed, 1 total
Tests:       7 passed, 7 total
Snapshots:   0 total
Time:        2.966s, estimated 3s