Assign the results of getClass() calls to unused variables

This works around a ReturnValueIgnored errorprone issue. There were several other places where this was already done, this is just catching up the remaining two places.

PiperOrigin-RevId: 671878499

src/google/protobuf/compiler/java/lite/enum_field.cc

@@ -111,7 +111,8 @@ void SetEnumVariables(
 
   // We use `x.getClass()` as a null check because it generates less bytecode
   // than an `if (x == null) { throw ... }` statement.
-  (*variables)["null_check"] = "value.getClass();\n";
+  (*variables)["null_check"] =
+      "java.lang.Class<?> unusedValueClass = value.getClass();\n";
   // Calls to Annotate() use variable ranges to know which text to annotate.
   (*variables)["{"] = "";
   (*variables)["}"] = "";

src/google/protobuf/compiler/java/lite/message_field.cc

@@ -88,7 +88,8 @@ void SetMessageVariables(
 
   // We use `x.getClass()` as a null check because it generates less bytecode
   // than an `if (x == null) { throw ... }` statement.
-  (*variables)["null_check"] = "value.getClass();\n";
+  (*variables)["null_check"] =
+      "java.lang.Class<?> unusedValueClass = value.getClass();\n";
   // Annotations often use { and } to determine ranges.
   (*variables)["{"] = "";
   (*variables)["}"] = "";