Add negative test for unquoted property string

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/20023)

test/property_test.c

@@ -194,6 +194,7 @@ static const struct {
     { 0, "a=abc,#@!, n=1" },    /* non-ASCII character located */
     { 1, "a='Hello" },          /* Unterminated string */
     { 0, "a=\"World" },         /* Unterminated string */
+    { 0, "a=_abd_" },           /* Unquoted string not starting with alphabetic */
     { 1, "a=2, n=012345678" },  /* Bad octal digit */
     { 0, "n=0x28FG, a=3" },     /* Bad hex digit */
     { 0, "n=145d, a=2" },       /* Bad decimal digit */