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/test/firehose_web/live/source_viewer_test.exs

@@ -25,8 +25,10 @@ defmodule FirehoseWeb.SourceViewerTest do
 
       assert has_element?(view, "#line-1"),
              "Line 1 should exist in the source viewer"
+
       assert has_element?(view, "#line-2"),
              "Line 2 should exist in the source viewer"
+
       assert has_element?(view, "#line-3"),
              "Line 3 should exist in the source viewer"
     end
@@ -54,10 +56,12 @@ defmodule FirehoseWeb.SourceViewerTest do
       expand_file(view, file)
 
       click_microprint_rect(view, file, 1)
+
       assert has_element?(view, "#line-1.sv-line-highlighted"),
              "Line 1 should be highlighted after first click"
 
       click_microprint_rect(view, file, 1)
+
       refute has_element?(view, "#line-1.sv-line-highlighted"),
              "Line 1 should no longer be highlighted after second click"
     end
@@ -66,7 +70,8 @@ defmodule FirehoseWeb.SourceViewerTest do
       files = MicroprintsLive.scan_source_files()
       file = List.first(files)
 
-      {:ok, view, _html} = live(conn, ~p"/microprints?expanded=#{file}&line=1&highlighted=#{file}")
+      {:ok, view, _html} =
+        live(conn, ~p"/microprints?expanded=#{file}&line=1&highlighted=#{file}")
 
       assert has_element?(view, "#line-1.sv-line-highlighted"),
              "Line 1 should be highlighted when restored from URL params"