fixup: add space before colon for base class declaration

Co-authored-by: Jan Schultke <[email protected]>

Author: dietmarkuehl

source/exec.tex

@@ -5721,7 +5721,7 @@
 \begin{codeblock}
 namespace std::execution {
   template<>
-  struct @\exposid{impls-for}@<affine_on_t>: @\exposid{default-impls}@ {
+  struct @\exposid{impls-for}@<affine_on_t> : @\exposid{default-impls}@ {
     static constexpr auto @\exposid{get-attrs}@ =
       [](const auto& data, const auto& child) noexcept -> decltype(auto) {
         return @\exposid{JOIN-ENV}@(@\exposid{SCHED-ATTRS}@(data), @\exposid{FWD-ENV}@(get_env(child)));