Fix credo quote-sigil warning in microprints_live_test.exs

Replace double-quoted string with escaped quotes in element selector
with a ~s sigil to satisfy Credo's 'More than 3 quotes found inside
string literal' readability check.

Includes formatting changes from mix format (ran via make check).

app/lib/firehose_web/live/microprints_live.ex

@@ -80,7 +80,8 @@ defmodule FirehoseWeb.MicroprintsLive do
                   highlighted_line={@highlighted_line}
                 />
 
-                <%= if @expanded_path == path and @source_lines do %>                  <.source_viewer
+                <%= if @expanded_path == path and @source_lines do %>
+                  <.source_viewer
                     source_lines={@source_lines}
                     highlighted_line={@highlighted_line}
                     language="elixir"
@@ -135,9 +136,12 @@ defmodule FirehoseWeb.MicroprintsLive do
 
     source_lines =
       case expanded do
-        nil -> nil
+        nil ->
+          nil
+
         ^path ->
           item = Enum.find(socket.assigns.microprints, &(&1.path == path))
+
           if item && item.source_dir do
             abs_path = resolve_source_path(item.source_dir, path)
             read_source(abs_path)
@@ -337,7 +341,12 @@ defmodule FirehoseWeb.MicroprintsLive do
   # Custom source_viewer with unique DOM IDs per file to prevent LiveView
   # DOM patching bugs when switching expanded files.
   def source_viewer(assigns) do
-    assigns = assign(assigns, :viewer_id, "source-viewer-" <> Integer.to_string(:erlang.phash2(assigns.file_path, 1_000_000)))
+    assigns =
+      assign(
+        assigns,
+        :viewer_id,
+        "source-viewer-" <> Integer.to_string(:erlang.phash2(assigns.file_path, 1_000_000))
+      )
 
     ~H"""
     <div
@@ -354,8 +363,8 @@ defmodule FirehoseWeb.MicroprintsLive do
             id={"line-#{num}"}
             class={"sv-line" <> if @highlighted_line == num, do: " sv-line-highlighted", else: ""}
           >
-            <span class="sv-line-number"><%= num %></span>
-            <span class="sv-line-content"><%= line %></span>
+            <span class="sv-line-number">{num}</span>
+            <span class="sv-line-content">{line}</span>
           </div>
         <% end %>
       </div>