replace | with || in string validation

Using short-circuiting operators makes it easier to perform some kinds
of source code analysis, like MC/DC code coverage (a requirement in
safety-critical environments). The optimized x86_64 assembly is
equivalent between the old and new versions.

Old assembly of that condition:

```
mov  rax, qword ptr [rdi + rdx + 8]
or   rax, qword ptr [rdi + rdx]
test rax, r9
je   .LBB0_7
```

New assembly of that condition:

```
mov  rax, qword ptr [rdi + rdx]
or   rax, qword ptr [rdi + rdx + 8]
test rax, r8
je   .LBB0_7
```

library/core/src/str/validations.rs

@@ -210,7 +210,7 @@ pub(super) fn run_utf8_validation(v: &[u8]) -> Result<(), Utf8Error> {
                         // break if there is a nonascii byte
                         let zu = contains_nonascii(*block);
                         let zv = contains_nonascii(*block.offset(1));
-                        if zu | zv {
+                        if zu || zv {
                             break;
                         }
                     }