pw_build: Rename python_script.gni to python_action.gni

Rename the python_script.gni file to python_action.gni to prepare to
rename the pw_python_script template.

An alias .gni file is created in separate change so that Git tracks this
as a file move rather than an update.

Change-Id: I812cf3bd73909593c5369c7437da16529e1a375a
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/22000
Reviewed-by: Alexei Frolov <frolv@google.com>
diff --git a/pw_protobuf_compiler/proto.gni b/pw_protobuf_compiler/proto.gni
index 899b561..c14d51b 100644
--- a/pw_protobuf_compiler/proto.gni
+++ b/pw_protobuf_compiler/proto.gni
@@ -15,7 +15,7 @@
 import("//build_overrides/pigweed.gni")
 
 import("$dir_pw_build/input_group.gni")
-import("$dir_pw_build/python_script.gni")
+import("$dir_pw_build/python_action.gni")
 import("$dir_pw_build/target_types.gni")
 import("$dir_pw_third_party/nanopb/nanopb.gni")