ToC block: Update link icon (#721)

* ToC block: Update link icon

* Use double quotes

Author: t-hamano

mu-plugins/blocks/table-of-contents/postcss/style.pcss

@@ -122,7 +122,7 @@
 			text-decoration: none !important;
 
 			/* stylelint-disable-next-line function-url-quotes */
-			background-image: url("data:image/svg+xml;charset=utf-8,%3Csvg xmlns=%27http://www.w3.org/2000/svg%27 width=%2724%27 height=%2713%27 fill=%27none%27%3E%3Cpath fill=%27%233858E9%27 fill-rule=%27evenodd%27 d=%27M10.083 9.91H6.32a3.069 3.069 0 0 1 0-6.139h3.764v1.5H6.32a1.569 1.569 0 0 0 0 3.138h3.764v1.5Zm3.834-6.138h3.764a3.069 3.069 0 0 1 0 6.137h-3.764v-1.5h3.764a1.569 1.569 0 0 0 0-3.137h-3.764zM9.333 7.304h5.334v-1.5H9.333z%27 clip-rule=%27evenodd%27/%3E%3C/svg%3E");
+			background-image: url("data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHZpZXdCb3g9IjAgMCAyNCAyNCI+PHBhdGggZmlsbD0iIzM4NThFOSIgZD0iTTEwIDE3LjM4OUg4LjQ0NEE1LjE5NCA1LjE5NCAwIDEgMSA4LjQ0NCA3SDEwdjEuNUg4LjQ0NGEzLjY5NCAzLjY5NCAwIDAgMCAwIDcuMzg5SDEwdjEuNVpNMTQgN2gxLjU1NmE1LjE5NCA1LjE5NCAwIDAgMSAwIDEwLjM5SDE0di0xLjVoMS41NTZhMy42OTQgMy42OTQgMCAwIDAgMC03LjM5SDE0VjdabS00LjUgNmg1di0xLjVoLTVWMTNaIj48L3BhdGg+PC9zdmc+");
 			background-position: right center;
 			background-repeat: no-repeat;
 			background-size: contain;