[3.15] gh-129813: Fix typo in byteswriter_resize() (GH-156938) (#156979)

gh-129813: Fix typo in byteswriter_resize() (GH-156938)

The intent is to test "resize and overallocate", even if in practice
"resize & overallocate" is the same (both variables are either 0 or
1). Use "&&" to better describe the intent of the test.
(cherry picked from commit 5141621)

Co-authored-by: Victor Stinner <vstinner@python.org>

Author: miss-islington

Objects/bytesobject.c

@@ -3629,7 +3629,7 @@ byteswriter_resize(PyBytesWriter *writer, Py_ssize_t size, int resize)
         return 0;
     }
 
-    if (resize & writer->overallocate) {
+    if (resize && writer->overallocate) {
         if (size <= (PY_SSIZE_T_MAX - size / OVERALLOCATE_FACTOR)) {
             size += size / OVERALLOCATE_FACTOR;
         }