chore: preserve current bazel glob behavior as bazel 8 changes the default value of allow_empty from True to False

PiperOrigin-RevId: 738900918

BUILD.bazel

@@ -1,9 +1,11 @@
 genrule(
-  name = "build_gen",
-  outs = ["build_gen.sh"],
-  executable = True,
-  srcs = glob(["run_build_gen.sh"]),
-  cmd = """
+    name = "build_gen",
+    srcs = glob(
+        ["run_build_gen.sh"],
+        allow_empty = True,
+    ),
+    outs = ["build_gen.sh"],
+    cmd = """
     if test -z \"$(SRCS)\"; then
       cat <<EOD > $@
 #!/bin/sh
@@ -15,4 +17,5 @@ EOD
       cp $(SRCS) $@
     fi
   """,
+    executable = True,
 )