Make the lock in CRYPTO_secure_actual_size a read lock

there is no operations within critical section that would
require write lock.

Signed-off-by: Nikola Pajkovsky <nikolap@openssl.org>

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
Reviewed-by: Viktor Dukhovni <viktor@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/28014)

crypto/mem_sec.c

@@ -278,7 +278,7 @@ size_t CRYPTO_secure_actual_size(void *ptr)
 #ifndef OPENSSL_NO_SECURE_MEMORY
     size_t actual_size;
 
-    if (!CRYPTO_THREAD_write_lock(sec_malloc_lock))
+    if (!CRYPTO_THREAD_read_lock(sec_malloc_lock))
         return 0;
     actual_size = sh_actual_size(ptr);
     CRYPTO_THREAD_unlock(sec_malloc_lock);