Test multi-line strings in interpolation (#789)

The behavior here is strange, and unintentional, but not obviously wrong.
Add a test to make sure I don't accidentally break it in the future.

src/lexer.rs

@@ -1431,6 +1431,22 @@ mod tests {
     ),
   }
 
+  test! {
+    name: interpolation_raw_multiline_string,
+    text: "hello:\n echo {{'\n'}}",
+    tokens: (
+      Identifier:"hello",
+      Colon,
+      Eol,
+      Indent:" ",
+      Text:"echo ",
+      InterpolationStart,
+      StringRaw:"'\n'",
+      InterpolationEnd,
+      Dedent,
+    ),
+  }
+
   test! {
     name: tokenize_names,
     text: "

tests/misc.rs

@@ -2452,6 +2452,19 @@ test! {
   ",
 }
 
+test! {
+  name: multi_line_string_in_interpolation,
+  justfile: "
+    foo:
+      echo {{'a
+      echo b
+      echo c'}}z
+      echo baz
+  ",
+  stdout: "a\nb\ncz\nbaz\n",
+  stderr: "echo a\n  echo b\n  echo cz\necho baz\n",
+}
+
 #[cfg(windows)]
 test! {
   name: windows_interpreter_path_no_base,