Fix up generated header include paths

The "hello_sapi" example lives in a different WORKSPACE as it is intended to
show how to embed SAPI in your own projects. However, this is not compatible
with simply running `bazel build //sandboxed_api/...` after checkout.

This change simply replace `copts = ["-I."]` with `includes = ["."]`, so that
generated headers can be found reliably, regardless of how the example is
compiled.

PiperOrigin-RevId: 313782756
Change-Id: Iac26e828146b01545c81d9500f5f68fa0f2d4ddf

sandboxed_api/examples/hello_sapi/BUILD.bazel

@@ -40,7 +40,7 @@ sapi_library(
 cc_binary(
     name = "hello",
     srcs = ["hello_main.cc"],
-    copts = ["-I."],  # To find the generated header
+    includes = ["."],  # To find the generated header
     deps = [":hello_sapi"],
 )
 
@@ -50,7 +50,7 @@ cc_binary(
 cc_binary(
     name = "hello_transacted",
     srcs = ["hello_transacted.cc"],
-    copts = ["-I."],  # To find the generated header
+    includes = ["."],  # To find the generated header
     deps = [
         ":hello_sapi",
         "@com_google_absl//absl/memory",