evp_test.c: There are now 3 parameters possible for digests

In digest_test_run() there are now 3 parameters possible plus
the sentinel value. In reality we will never use all three
at once but Coverity rightfully complains that it is possible
to overflow the params array.

Fixes Coverity 1548054

Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from #22521)

test/evp_test.c

@@ -458,7 +458,7 @@ static int digest_test_run(EVP_TEST *t)
     unsigned int got_len;
     size_t size = 0;
     int xof = 0;
-    OSSL_PARAM params[3], *p = &params[0];
+    OSSL_PARAM params[4], *p = &params[0];
 
     t->err = "TEST_FAILURE";
     if (!TEST_ptr(mctx = EVP_MD_CTX_new()))