ESQL: Update function tests (#119586)

Updates our function tests now that type signatures are required for all
signatures under test.

Author: nik9000

x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/TestCaseSupplier.java

@@ -110,13 +110,11 @@ public static List<TestCaseSupplier> stringCases(
     @Override
     public TestCase get() {
         TestCase supplied = supplier.get();
-        if (types != null) {
-            for (int i = 0; i < types.size(); i++) {
-                if (supplied.getData().get(i).type() != types.get(i)) {
-                    throw new IllegalStateException(
-                        name + ": supplier/data type mismatch " + supplied.getData().get(i).type() + "/" + types.get(i)
-                    );
-                }
+        for (int i = 0; i < types.size(); i++) {
+            if (supplied.getData().get(i).type() != types.get(i)) {
+                throw new IllegalStateException(
+                    name + ": supplier/data type mismatch " + supplied.getData().get(i).type() + "/" + types.get(i)
+                );
             }
         }
         return supplied;