rpmbuild: fix chroot_scan copying
    
    We are getting a following error
    
        Traceback (most recent call last):
        File "/usr/bin/copr-rpmbuild", line 128, in main
    	action(args, config)
        File "/usr/bin/copr-rpmbuild", line 220, in build_srpm
    	produce_srpm(task, config, resultdir)
        File "/usr/bin/copr-rpmbuild", line 164, in produce_srpm
    	shutil.copy(os.path.join(tempdir, item), resultdir)
        File "/usr/lib64/python3.9/shutil.py", line 415, in copy
    	copyfile(src, dst, follow_symlinks=follow_symlinks)
        File "/usr/lib64/python3.9/shutil.py", line 261, in copyfile
    	with open(src, 'rb') as fsrc, open(dst, 'wb') as fdst:
        IsADirectoryError: [Errno 21] Is a directory: '/tmp/copr-rpmbuild-nmb0t13y/chroot_scan'
    
    Indeed we cannot copy directories with `shutil.copy` function
    
        >>> import os
        >>> import shutil
        >>> os.makedirs("/tmp/testcopydir")
        >>> shutil.copy("/tmp/testcopydir", "/tmp/testcopydir2")
        IsADirectoryError: [Errno 21] Is a directory: '/tmp/testcopydir'
    
    We have been copying `chroot_scan` for final RPMs for years but so far
    we didn't do it for SRPM builds.