"PHP Update Required" dashboard box title is right-aligned

[SergeyBiryukov]

As noted by @TimothyBlynJacobs on ​Slack, the "PHP Update Required" title is now right-aligned.

This is a regression in trunk, see the screenshots.

Additionally:

• The "Learn more" button has some extra bottom padding, due to removing !important from here in [48129]:

  .postbox .inside > p:last-child,
  .rss-widget ul li:last-child {
      margin-bottom: 1px !important;
  }
  

• The vertical alignment on that button looks off.

[SergeyBiryukov]

In WordPress 5.4

[whyisjake]

Fix for both the headline and the bottom margin.

[SergeyBiryukov]

Instead of adding more styles, I'd rather restore the removed !important piece here, since it seems that could also affect other things.

Could we track down the commit that made the title right-aligned?

[sabernhardt]

The alignment is from [48373], using CSS flexbox on the heading for edit-box links.

.postbox-header .hndle {
	flex-grow: 1;
	/* Handle the alignment for the configurable dashboard widgets "Configure" edit-box link. */
	display: flex;
	justify-content: space-between;
	align-items: center;
}

[SergeyBiryukov]

In 48671:

Administration: Correct alignment of the "PHP Update Required" dashboard box title.

Restore one instance of !important CSS rule for backward compatibility.

Follow-up to [48129], [48373].

Props whyisjake, sabernhardt, TimothyBlynJacobs, SergeyBiryukov.
Fixes #50788.