chore: fix tabindex capitalization

The Svelte Language server does not detect `tabIndex` as a valid attribute.

Note, however, that `tabIndex` is correct when using it in JavaScript (e.g., `node.tabIndex`).

src/ListBox/ListBoxSelection.svelte

@@ -62,7 +62,7 @@
     <div
       bind:this="{ref}"
       role="button"
-      tabIndex="{disabled ? -1 : 0}"
+      tabindex="{disabled ? -1 : 0}"
       class:bx--tag__close-icon="{true}"
       on:click|preventDefault|stopPropagation="{(e) => {
         if (!disabled) {

src/Tooltip/Tooltip.svelte

@@ -254,7 +254,7 @@
         on:click|stopPropagation
         on:mousedown|stopPropagation
         class:bx--tooltip__content="{true}"
-        tabIndex="-1"
+        tabindex="-1"
         role="dialog"
       >
         <slot />