Valgrind: fix "definitely lost" memory in test - test-userdata-dir-invalid-home

==66427== 128 bytes in 1 blocks are definitely lost in loss record 22 of 25
==66427==    at 0x4843738: malloc (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==66427==    by 0x49B85EF: g_realloc (in /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0.7600.1)
==66427==    by 0x49D6EF1: ??? (in /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0.7600.1)
==66427==    by 0x49D6F6F: g_string_sized_new (in /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0.7600.1)
==66427==    by 0x499AB00: ??? (in /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0.7600.1)
==66427==    by 0x499B2D8: g_build_filename (in /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0.7600.1)
==66427==    by 0x10A498: main (test-userdata-dir-invalid-home.c:74)
==66427==

libgnucash/core-utils/test/test-userdata-dir-invalid-home.c

@@ -83,6 +83,8 @@ main(G_GNUC_UNUSED int argc, G_GNUC_UNUSED char **argv)
      * The code should fall back to using the temporary
      * directory in that case. */
     g_setenv("HOME", homedir, TRUE);
+    g_free (homedir);
+
     for (i = 0; strs2[i].funcname != NULL; i++)
     {
         char *daout;