stdexec: update to later commit

The upstream code has done some namespace changes.  Point to a commit
in that timeframe and fix up the local usages in order to compile
successfully.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I5a21ccd0774ee5cd22d45c9a425e43560734a571
diff --git a/test/async/task.cpp b/test/async/task.cpp
index 6ee90f8..a7e5a15 100644
--- a/test/async/task.cpp
+++ b/test/async/task.cpp
@@ -17,7 +17,7 @@
     EXPECT_FALSE(value);
 
     // Run it and confirm the value is updated.
-    std::this_thread::sync_wait(t());
+    stdexec::this_thread::sync_wait(t());
     EXPECT_TRUE(value);
 }
 
@@ -41,7 +41,7 @@
     // Add boolean to confirm that co-routine actually executed by the
     // end.
     bool executed = false;
-    std::this_thread::sync_wait(_::two(executed));
+    stdexec::this_thread::sync_wait(_::two(executed));
     EXPECT_TRUE(executed);
 }
 
@@ -69,11 +69,11 @@
     };
 
     // Ensure throws surface up.
-    EXPECT_THROW(std::this_thread::sync_wait(_::one()), std::logic_error);
+    EXPECT_THROW(stdexec::this_thread::sync_wait(_::one()), std::logic_error);
 
     // Ensure throws can be caught inside a co-routine.
     bool caught = false;
-    std::this_thread::sync_wait(_::two(caught));
+    stdexec::this_thread::sync_wait(_::two(caught));
     EXPECT_TRUE(caught);
 }
 
@@ -88,16 +88,16 @@
                 ++executed;
                 co_return (co_await one(count - 1, executed)) + 1;
             }
-            co_return co_await std::execution::just(0);
+            co_return co_await stdexec::just(0);
         }
     };
 
     static constexpr size_t count = 100;
     size_t executed = 0;
 
-    std::this_thread::sync_wait(
+    stdexec::this_thread::sync_wait(
         _::one(count, executed) |
-        std::execution::then([=](auto result) { EXPECT_EQ(result, count); }));
+        stdexec::then([=](auto result) { EXPECT_EQ(result, count); }));
 
     EXPECT_EQ(executed, count);
 }