fix the makefile

On other projects where we are using `BuildMethod: makefile`
we are just making a dependencies layer, so its ok for the
Makefile to just install packages.

On this project there is no dependency layer so if we
switch the `BuildMethod` to `makefile` the makefile is
also responsible for copying the application code into
the zip artifact.

postcode_lookup/Makefile

@@ -1,7 +1,9 @@
 build-ECPostcodeLookupFunction:
+	cp --recursive . "$(ARTIFACTS_DIR)/"
 	pip install --break-system-packages setuptools
-	pip install --upgrade -r requirements.txt --target "$(ARTIFACTS_DIR)/python/"
+	pip install --upgrade -r requirements.txt --target "$(ARTIFACTS_DIR)/"
 
 build-BasicAuthFunction:
+	cp --recursive . "$(ARTIFACTS_DIR)/"
 	pip install --break-system-packages setuptools
-	pip install --upgrade -r requirements.txt --target "$(ARTIFACTS_DIR)/python/"
+	pip install --upgrade -r requirements.txt --target "$(ARTIFACTS_DIR)/"