nanopb: Fix self-inclusive src

Fixes issue described in #301014

pkgs/development/libraries/nanopb/test-message-with-annotations/default.nix

@@ -1,9 +1,12 @@
-{ stdenv, protobuf, nanopb }:
+{ lib, stdenv, protobuf, nanopb }:
 
 stdenv.mkDerivation {
   name = "nanopb-test-message-with-annotations";
   meta.timeout = 60;
-  src = ./.;
+  src = lib.fileset.toSource {
+    root = ./.;
+    fileset = lib.fileset.unions [ ./withannotations.proto ];
+  };
 
   # protoc requires any .proto file to be compiled to reside within it's
   # proto_path. By default the current directory is automatically added to the

pkgs/development/libraries/nanopb/test-message-with-options/default.nix

@@ -1,9 +1,15 @@
-{ stdenv, protobuf, nanopb }:
+{ lib, stdenv, protobuf, nanopb }:
 
 stdenv.mkDerivation {
   name = "nanopb-test-message-with-options";
   meta.timeout = 60;
-  src = ./.;
+  src = lib.fileset.toSource {
+    root = ./.;
+    fileset = lib.fileset.unions [
+      ./withoptions.proto
+      ./withoptions.options
+    ];
+  };
 
   # protoc requires any .proto file to be compiled to reside within it's
   # proto_path. By default the current directory is automatically added to the

pkgs/development/libraries/nanopb/test-simple-proto2/default.nix

@@ -1,9 +1,12 @@
-{ stdenv, protobuf, nanopb }:
+{ lib, stdenv, protobuf, nanopb }:
 
 stdenv.mkDerivation {
   name = "nanopb-test-simple-proto2";
   meta.timeout = 60;
-  src = ./.;
+  src = lib.fileset.toSource {
+    root = ./.;
+    fileset = lib.fileset.unions [ ./simple.proto ];
+  };
 
   # protoc requires any .proto file to be compiled to reside within it's
   # proto_path. By default the current directory is automatically added to the

pkgs/development/libraries/nanopb/test-simple-proto3/default.nix

@@ -1,10 +1,12 @@
-{ stdenv, protobuf, nanopb }:
+{ lib, stdenv, protobuf, nanopb }:
 
 stdenv.mkDerivation {
   name = "nanopb-test-simple-proto3";
   meta.timeout = 60;
-  src = ./.;
-
+  src = lib.fileset.toSource {
+    root = ./.;
+    fileset = lib.fileset.unions [ ./simple.proto ];
+  };
   # protoc requires any .proto file to be compiled to reside within it's
   # proto_path. By default the current directory is automatically added to the
   # proto_path. I tried using --proto_path ${./.} ${./simple.proto} and it did