Fixup indent in codeblock to standard 2 spaces

Author: mattkretz

source/numerics.tex

@@ -18705,10 +18705,10 @@
 \begin{codeblock}
 template<@\exposid{simd-size-type}@ I>
 typename V::value_type @\exposid{perm-fn}@() {
-    constexpr auto src_index = @\exposid{gen-fn}@(I);
-    if constexpr (src_index == zero_element) return typename V::value_type();
-    else if constexpr (src_index == uninit_element) return @\exposid{unspecified-value}@;
-    else return v[src_index];
+  constexpr auto src_index = @\exposid{gen-fn}@(I);
+  if constexpr (src_index == zero_element) return typename V::value_type();
+  else if constexpr (src_index == uninit_element) return @\exposid{unspecified-value}@;
+  else return v[src_index];
 }
 \end{codeblock}
 \end{itemize}