documentation seems to use bad postbuild_arch example

There seems to be a bad example for postbuild_arch in the recipe documentation. It should call postbuild_arch instead of build_arch:

```
diff --git a: doc/source/recipes.rst b: doc/source/recipes.rst
index b6e34319..c5097cb9 100644
--- a: doc/source/recipes.rst
+++ b: doc/source/recipes.rst
@@ -88,7 +88,7 @@ The actual build process takes place via three core methods::
# Do the main recipe build

def postbuild_arch(self, arch):
- super().build_arch(arch)
+ super().postbuild_arch(arch)
# Do any clearing up

$ git describe --tags --dirty --always
v2024.01.21-250-g2f107b15-dirty
```

Open doc/source/recipes.rst and inspect the postbuild_arch example around the recipe build methods. Update the example so it calls postbuild_arch rather than build_arch, then review the rendered recipe documentation to confirm the example is correct.

Written by the indexing model from the issue text.