Require the "command" param of run_shell is a string

This constitutes an incompatible change guarded by flag --incompatible_run_shell_command_string.

Progress toward #5903.

RELNOTES: The `command` parameter of the `actions.run_shell()` function will be restricted to only accept strings (and not string sequences). This check is attached to flag `--incompatible_run_shell_command_string`. One may migrate by using the `arguments` parameter of `actions.run()` instead. See https://github.com/bazelbuild/bazel/issues/5903 for more info.
PiperOrigin-RevId: 253122136
diff --git a/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java b/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java
index 341eea1..72ece5b 100644
--- a/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java
+++ b/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java
@@ -161,6 +161,7 @@
         "--incompatible_remap_main_repo=" + rand.nextBoolean(),
         "--incompatible_remove_native_maven_jar=" + rand.nextBoolean(),
         "--incompatible_restrict_named_params=" + rand.nextBoolean(),
+        "--incompatible_run_shell_command_string=" + rand.nextBoolean(),
         "--incompatible_string_join_requires_strings=" + rand.nextBoolean(),
         "--incompatible_restrict_string_escapes=" + rand.nextBoolean(),
         "--internal_skylark_flag_test_canary=" + rand.nextBoolean());
@@ -212,6 +213,7 @@
         .incompatibleRemapMainRepo(rand.nextBoolean())
         .incompatibleRemoveNativeMavenJar(rand.nextBoolean())
         .incompatibleRestrictNamedParams(rand.nextBoolean())
+        .incompatibleRunShellCommandString(rand.nextBoolean())
         .incompatibleStringJoinRequiresStrings(rand.nextBoolean())
         .incompatibleRestrictStringEscapes(rand.nextBoolean())
         .internalSkylarkFlagTestCanary(rand.nextBoolean())