fix: small accessibility fix for IATI logos in header and footer

Added ARIA labels to the IATI logo links in the header and footer
and null alt text attributes to the img tags to improve accessibility.

Author: chrisarridge

src/scss/layout/footer/footer.stories.ts

@@ -14,10 +14,11 @@ export const Footer: Story = {
   render: (args) => html`
     <footer class="iati-footer">
       <div>
-        <a href="https://iatistandard.org/">
+        <a href="https://iatistandard.org/" aria-label="Go to IATI homepage">
           <img
             src="http://styles.iatistandard.org/assets/svg/source/logo-white.svg"
             class="iati-footer__logo"
+            alt=""
           />
         </a>
         <div class="iati-footer__list">

src/scss/layout/header/header.stories.ts

@@ -12,10 +12,11 @@ export const Header: Story = {
   render: () => html`
     <header class="iati-header">
       <div>
-        <a href="https://iatistandard.org/">
+        <a href="https://iatistandard.org/" aria-label="Go to IATI homepage">
           <img
             src="http://styles.iatistandard.org/assets/svg/source/logo-colour.svg"
             class="iati-header__logo"
+            alt=""
           />
         </a>
       </div>