fix: revert accidental schema changes

In:
ec06326#diff

I refactored the schemas to use a description. I accidentally changed
two keys (one Required->Optional, the other Optional->Required).

This was supposed to be a doc only change, so let's revert them back to
the way they were.

Author: ahal

src/taskgraph/transforms/run/__init__.py

@@ -153,7 +153,7 @@
             Extra: object,
         },
         Required("worker-type"): task_description_schema["worker-type"],
-        Required(
+        Optional(
             "worker",
             description=dedent(
                 """

src/taskgraph/transforms/run/toolchain.py

@@ -97,7 +97,7 @@
                 """
             ),
         ): {str: object},
-        Optional(
+        Required(
             "workdir",
             description=dedent(
                 """