Fix Cover width regression

[jasmussen]

In #25103 I introduced a regression to the cover block on the frontend (ironically in fixing another regression). This was kindly pointed out by @johnstonphilip in #25103 (comment) and #24523. Sorry about that.

This PR should address the regression, but also keep the fix for the initial issue (the width is now plainly 100% rather than calc(100% - 70px)).

Here's before and after for me in the editor:

Here's the frontend showing the width property present for the inner container:

[aristath]

👍 Thank you for the quick fix!
LGTM.

[github-actions]

Size Change: +4 B (0%)

Total Size: 1.19 MB

Filename	Size	Change
build/block-library/style-rtl.css	7.71 kB	+2 B (0%)
build/block-library/style.css	7.71 kB	+2 B (0%)

ℹ️ View Unchanged

Filename	Size	Change
build/a11y/index.js	1.14 kB	0 B
build/annotations/index.js	3.54 kB	0 B
build/api-fetch/index.js	3.35 kB	0 B
build/autop/index.js	2.72 kB	0 B
build/blob/index.js	668 B	0 B
build/block-directory/index.js	8.6 kB	0 B
build/block-directory/style-rtl.css	943 B	0 B
build/block-directory/style.css	942 B	0 B
build/block-editor/index.js	130 kB	0 B
build/block-editor/style-rtl.css	10.9 kB	0 B
build/block-editor/style.css	10.9 kB	0 B
build/block-library/editor-rtl.css	8.65 kB	0 B
build/block-library/editor.css	8.65 kB	0 B
build/block-library/index.js	143 kB	0 B
build/block-library/theme-rtl.css	741 B	0 B
build/block-library/theme.css	741 B	0 B
build/block-serialization-default-parser/index.js	1.78 kB	0 B
build/block-serialization-spec-parser/index.js	3.1 kB	0 B
build/blocks/index.js	47.6 kB	0 B
build/components/index.js	169 kB	0 B
build/components/style-rtl.css	15.4 kB	0 B
build/components/style.css	15.4 kB	0 B
build/compose/index.js	9.63 kB	0 B
build/core-data/index.js	12.1 kB	0 B
build/data-controls/index.js	684 B	0 B
build/data/index.js	8.63 kB	0 B
build/date/index.js	31.9 kB	0 B
build/deprecated/index.js	772 B	0 B
build/dom-ready/index.js	569 B	0 B
build/dom/index.js	4.43 kB	0 B
build/edit-navigation/index.js	10.6 kB	0 B
build/edit-navigation/style-rtl.css	868 B	0 B
build/edit-navigation/style.css	871 B	0 B
build/edit-post/index.js	306 kB	0 B
build/edit-post/style-rtl.css	6.3 kB	0 B
build/edit-post/style.css	6.29 kB	0 B
build/edit-site/index.js	21.1 kB	0 B
build/edit-site/style-rtl.css	3.77 kB	0 B
build/edit-site/style.css	3.77 kB	0 B
build/edit-widgets/index.js	21.4 kB	0 B
build/edit-widgets/style-rtl.css	2.97 kB	0 B
build/edit-widgets/style.css	2.97 kB	0 B
build/editor/editor-styles-rtl.css	480 B	0 B
build/editor/editor-styles.css	482 B	0 B
build/editor/index.js	42.5 kB	0 B
build/editor/style-rtl.css	3.85 kB	0 B
build/editor/style.css	3.84 kB	0 B
build/element/index.js	4.45 kB	0 B
build/escape-html/index.js	733 B	0 B
build/format-library/index.js	7.49 kB	0 B
build/format-library/style-rtl.css	547 B	0 B
build/format-library/style.css	548 B	0 B
build/hooks/index.js	1.74 kB	0 B
build/html-entities/index.js	622 B	0 B
build/i18n/index.js	3.54 kB	0 B
build/is-shallow-equal/index.js	709 B	0 B
build/keyboard-shortcuts/index.js	2.39 kB	0 B
build/keycodes/index.js	1.85 kB	0 B
build/list-reusable-blocks/index.js	3.02 kB	0 B
build/list-reusable-blocks/style-rtl.css	476 B	0 B
build/list-reusable-blocks/style.css	476 B	0 B
build/media-utils/index.js	5.12 kB	0 B
build/notices/index.js	1.69 kB	0 B
build/nux/index.js	3.27 kB	0 B
build/nux/style-rtl.css	671 B	0 B
build/nux/style.css	668 B	0 B
build/plugins/index.js	2.44 kB	0 B
build/primitives/index.js	1.34 kB	0 B
build/priority-queue/index.js	789 B	0 B
build/redux-routine/index.js	2.85 kB	0 B
build/reusable-blocks/index.js	3.04 kB	0 B
build/rich-text/index.js	13 kB	0 B
build/server-side-render/index.js	2.6 kB	0 B
build/shortcode/index.js	1.7 kB	0 B
build/token-list/index.js	1.24 kB	0 B
build/url/index.js	4.07 kB	0 B
build/viewport/index.js	1.75 kB	0 B
build/warning/index.js	1.13 kB	0 B
build/wordcount/index.js	1.17 kB	0 B

_{compressed-size-action}

[jasmussen]

Thanks for the review!