ensure ibf_load_setup is only passed String params

In cases where RubyVM::InstructionSequence.load_from_binary() is
passed a param other than a String, we attempt to call the
RSTRING_LENINT macro on it which can cause a segfault.

ex:
```
var_0 = 0
RubyVM::InstructionSequence.load_from_binary(var_0)
```

This commit adds a type check to raise unless we are provided
a String.

compile.c

@@ -14214,6 +14214,8 @@ ibf_load_setup_bytes(struct ibf_load *load, VALUE loader_obj, const char *bytes,
 static void
 ibf_load_setup(struct ibf_load *load, VALUE loader_obj, VALUE str)
 {
+    StringValue(str);
+
     if (RSTRING_LENINT(str) < (int)sizeof(struct ibf_header)) {
         rb_raise(rb_eRuntimeError, "broken binary format");
     }

test/ruby/test_iseq.rb

@@ -850,4 +850,11 @@ class TestISeq < Test::Unit::TestCase
       RubyVM::InstructionSequence.compile_prism(Object.new)
     end
   end
+
+  def test_load_from_binary_only_accepts_string_param
+    assert_raise(TypeError) do
+      var_0 = 0
+      RubyVM::InstructionSequence.load_from_binary(var_0)
+    end
+  end
 end