fix crash in ecp_nistz256_point_add_affine()

The .rodata section with precomputed constant `ecp_nistz256_precomputed` needs to be
terminated by .text, because the ecp_nistz256_precomputed' happens to be the
first section in the file. The lack of .text makes code to arrive into the same
.rodata section where ecp_nistz256_precomputed is found. The exception is raised
as soon as CPU attempts to execute the code from read only section.

Fixes #24184

crypto/ec/asm/ecp_nistz256-x86_64.pl

@@ -4736,6 +4736,7 @@ ()
 }
 print <<___;
 .size	ecp_nistz256_precomputed,.-ecp_nistz256_precomputed
+.text
 ___
 
 $code =~ s/\`([^\`]*)\`/eval $1/gem;