feat: Add `git-merge` icon

icons/git-merge.svg

+<svg
+  xmlns="http://www.w3.org/2000/svg"
+  width="24"
+  height="24"
+  viewBox="0 0 24 24"
+  fill="none"
+  stroke="currentColor"
+  stroke-width="2"
+  stroke-linecap="round"
+  stroke-linejoin="round"
+>
+  <circle cx="18" cy="18" r="3" />
+  <circle cx="6" cy="6" r="3" />
+  <path d="M6 21V9a9 9 0 0 0 9 9" />
+</svg>