C++: Prepare experimental_cc_shared_library for cc_library change

linked_statically_by attribute in cc_library will have a nodep label type
instead of a string type.

RELNOTES:none
PiperOrigin-RevId: 289665470
Change-Id: Ic86f3cd0fecf1ad8befb21844c0d7176dc898934
diff --git a/examples/experimental_cc_shared_library.bzl b/examples/experimental_cc_shared_library.bzl
index 0e30bde..b54ecc7 100644
--- a/examples/experimental_cc_shared_library.bzl
+++ b/examples/experimental_cc_shared_library.bzl
@@ -282,7 +282,7 @@
 
     linked_statically_by = []
     if hasattr(ctx.rule.attr, "linked_statically_by"):
-        linked_statically_by = ctx.rule.attr.linked_statically_by
+        linked_statically_by = [str(label) for label in ctx.rule.attr.linked_statically_by]
 
     return [GraphNodeInfo(
         label = str(ctx.label),