Fix spacing in docs for tarfile (GH-20629)

Before
```
content.txt is 42 bytes in size and isa regular file.
folder is 420 bytes in size and isa directory.
magic is 4200 bytes in size and issomething else.
```

After:
```
content.txt is 42 bytes in size and is a regular file.
folder is 420 bytes in size and is a directory.
magic is 4200 bytes in size and is something else.
```

Automerge-Triggered-By: @orsenthil