tests: use <fcntl.h> instead of <sys/fcntl.h>

When building on musl, we get:
```
In file included from tests/zfs-tests/cmd/getversion.c:22:
/usr/include/sys/fcntl.h:1:2: error: #warning redirecting incorrect #include <sys/fcntl.h> to <fcntl.h> [-Werror=cpp]
    1 | #warning redirecting incorrect #include <sys/fcntl.h> to <fcntl.h>
      |  ^~~~~~~
```

There's some other use of <sys/fcntl.h> in the codebase, but they're on the
module side, where libspl seems to handle it all, so not touching that.

Bug: https://bugs.gentoo.org/925235
Signed-off-by: Sam James <[email protected]>

tests/zfs-tests/cmd/getversion.c

@@ -19,9 +19,9 @@
  */
 
 #include <sys/ioctl.h>
-#include <sys/fcntl.h>
 #include <linux/fs.h>
 #include <err.h>
+#include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>