Make skylib a dev dependency

Author: martis42

MODULE.bazel

@@ -4,10 +4,6 @@ module(
     bazel_compatibility = [">=5.4.0"],
 )
 
-bazel_dep(
-    name = "bazel_skylib",
-    version = "1.5.0",
-)
 bazel_dep(
     name = "rules_cc",
     version = "0.0.8",
@@ -30,6 +26,12 @@ use_repo(non_module_dependencies, "dwyu_pcpp")
 ### Development Dependencies
 ###
 
+bazel_dep(
+    name = "bazel_skylib",
+    version = "1.5.0",
+    dev_dependency = True,
+)
+
 python = use_extension(
     "@rules_python//python/extensions:python.bzl",
     "python",