Unify dividing line color in commit info-well

What does this MR do and why?

Unify dividing line color in commit info-well

The lines that divide the sections of the info-well that holds the details about a commit did not match each other.
This makes them all 1px solid $well-inner-border

Why do it this way?

You may ask:

Why not just apply .well-segment to the divs inside the .info-well so that they would have the same border as the other .well-segments?

We could

• add well-segment to this div, and
• remove the classes that mimic it from this div

... then we'd have a matching border, but only one row for both branches and tags:

So we'd need two well-segments, but then we'd need a container div around them because every component must have a single root element (which is not true in Vue 3 but we haven't made it to Vue 3 yet), but then the styling that applies the bottom border to every well-segment except for the last one in the group breaks because the well-segments are in two nested groups:

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Why not adjust the gl-border-* class to match the existing border?

The bottom border of the well-segment is defined as $well-inner-border: #eef0f2 in variables.scss for light mode and overridden as $gray-200 in _dark.scss for dark mode.

We could use gl-border-gray-200 instead of gl-border-gray-50 to fix this in dark mode, but that would break it in light mode because #eef0f2 is not equivalent to $gray-200 in light mode:

dark	light

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Why replace gl-border-b with gl-border-b-solid gl-border-b-1?

gl-border-b also sets a border color, which turns out to be #dcdcde in light mode and #434248 in dark mode, neither of which are what we want. If we separately set the bottom border style to solid with gl-border-b-solid and the border width to 1 with gl-border-b-1, then it will keep the border-color we set in the stylesheet to match the other border colors.

MR acceptance checklist

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Screenshots or screen recordings

Scenario	Before	After
dark mode	some lines are #535158 ($well-inner-border), others are #333238 (gl-border-gray-50)	all lines should be #535158 ($well-inner-border)
dark mode, just branches
dark mode, branches and tags
light mode	some lines are #eef0f2 ($well-inner-border), others are #ececef (gl-border-gray-50)	all lines should be #eef0f2 ($well-inner-border)
light mode, just branches
light mode, branches and tags

How to set up and validate locally

0. git checkout master
1. make a commit and navigate to it in the UI
2. observe the difference in dividing lines in the info box - the line below the commit's parent is more prominent than the line below the commit's related branches - the difference is more noticeable in dark mode
3. git checkout mfluharty-even-out-commit-refs-lines
4. the lines dividing each section of the commit information should be consistent