BUG #18057: unaccent removes intentional spaces

The following bug has been logged on the website:

Bug reference:      18057
Logged by:          Martin Schlossarek
Email address:      martin@schlossarek.me
PostgreSQL version: 15.1
Operating system:   Fedora 38
Description:

I discovered that the unaccent extension also removes intentional spaces
that are explicitly specified in the accent.rules. As far as I see it
correctly, all fraction characters are affected, for example:

```sql
# select unaccent('1½');
--- expected output: 1 1/2
--- actual output: 11/2
```

Affected characters:
```bash
$ curl -s
"https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob_plain;f=contrib/unaccent/unaccent.rules;hb=HEAD"
| grep -E " "
¼        1/4
½        1/2
¾        3/4
⅐        1/7
⅑        1/9
⅒        1/10
⅓        1/3
⅔        2/3
⅕        1/5
⅖        2/5
⅗        3/5
⅘        4/5
⅙        1/6
⅚        5/6
⅛        1/8
⅜        3/8
⅝        5/8
⅞        7/8
⅟        1/
↉        0/3
```