Extension page WCAG fails: contrast and text alternative

The WCAG automatic tests found out some regressions in the extension interface.
I couldn't find quickly why this happens. AFAIU, the UI that triggers those violations existed for a long time, the reports only appeared recently, probably because the tests were updated.

Here are the relevant information. Both are regressions:

1: Links must have discernible text
Description: Ensure links have discernible text
Help URL: https://dequeuniversity.com/rules/axe/4.11/link-name?application=axeAPI
Help: Links must have discernible text
Impact: serious
Tags: cat.name-role-value, wcag2a, wcag244, wcag412, section508, section508.22.a, TTv5, TT6.a, EN-301-549, EN-9.2.4.4, EN-9.4.1.2, ACT, RGAAv4, RGAA-6.2.1

HTML element:
<a href="#dropDownMenu" class="dropdown-toggle secondary" tabindex="0"><span></span></a>
Selector: [.extension-item-installed-dependency.extension-item[method="post"]:nth-child(3) > .extension-header > .extension-actions > .button-group.initialized.buttonwrapper > .dropdown-toggle.secondaryhref$="#dropDownMenu"]
Fix all of the following:
Element is in tab order and does not have accessible text

Fix any of the following:
Element does not have text that is visible to screen readers
aria-label attribute does not exist or is empty
aria-labelledby attribute does not exist, references elements that do not exist or references elements that are empty
Element has no title attribute

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Validation in the test method [testRepositorySelector]
Check for [org.xwiki.extension.test.po.ExtensionAdministrationPage] at http://xwikiweb0:8080/xwiki/bin/admin/XWiki/XWikiPreferences?section=XWiki.Extensions&search=alice&repo=&recommended=on&recommended=false&indexed=false&compatible=on&compatible=false.
Found [1] items

1: Elements must meet minimum color contrast ratio thresholds
Description: Ensure the contrast between foreground and background colors meets WCAG 2 AA minimum contrast ratio thresholds
Help URL: https://dequeuniversity.com/rules/axe/4.11/color-contrast?application=axeAPI
Help: Elements must meet minimum color contrast ratio thresholds
Impact: serious
Tags: cat.color, wcag2aa, wcag143, TTv5, TT13.c, EN-301-549, EN-9.1.4.3, ACT, RGAAv4, RGAA-3.2.1

HTML element:
<a href="#extension-search-advanced-body">Advanced search</a>
Selector: [legend > a]
Fix any of the following:
Element has insufficient color contrast of 4.44 (foreground color: #2f70a7, background color: #ececec, font size: 7.4pt (9.8px), font weight: normal). Expected contrast ratio of 4.5:1