test/ca-fd-leak: fix clang-tidy lints

(cherry picked from commit b050db951b)

tests/nixos/ca-fd-leak/sender.c

@@ -19,7 +19,7 @@ int main(int argc, char **argv) {
     struct sockaddr_un data;
     data.sun_family = AF_UNIX;
     data.sun_path[0] = 0;
-    strcpy(data.sun_path + 1, argv[1]);
+    strncpy(data.sun_path + 1, argv[1], sizeof(data.sun_path) - 2);
 
     // Now try to connect, To ensure we work no matter what order we are
     // executed in, just busyloop here.

tests/nixos/ca-fd-leak/smuggler.c

@@ -5,6 +5,7 @@
 #include <stdio.h>
 #include <unistd.h>
 #include <assert.h>
+#include <string.h>
 
 int main(int argc, char **argv) {