Fix bazel incompatible changes

When building grpc with the upcoming `--incompatible_depset_is_not_iterable` flag, these violations were found

bazel/generate_cc.bzl

@@ -41,11 +41,11 @@ def _join_directories(directories):
 
 def generate_cc_impl(ctx):
     """Implementation of the generate_cc rule."""
-    protos = [f for src in ctx.attr.srcs for f in src.proto.check_deps_sources]
+    protos = [f for src in ctx.attr.srcs for f in src.proto.check_deps_sources.to_list()]
     includes = [
         f
         for src in ctx.attr.srcs
-        for f in src.proto.transitive_imports
+        for f in src.proto.transitive_imports.to_list()
     ]
     outs = []
     proto_root = get_proto_root(
@@ -128,7 +128,7 @@ def generate_cc_impl(ctx):
             arguments += ["-I{0}".format(f + "/../..")]
             well_known_proto_files = [
                 f
-                for f in ctx.attr.well_known_protos.files
+                for f in ctx.attr.well_known_protos.files.to_list()
             ]
 
     ctx.actions.run(

bazel/python_rules.bzl

@@ -33,7 +33,7 @@ def _generate_py_impl(context):
     includes = [
         file
         for src in context.attr.deps
-        for file in src.proto.transitive_imports
+        for file in src.proto.transitive_imports.to_list()
     ]
     proto_root = get_proto_root(context.label.workspace_root)
     format_str = (_GENERATED_GRPC_PROTO_FORMAT if context.executable.plugin else _GENERATED_PROTO_FORMAT)