[DoctrineBridge] Fix empty parameter logging in the dbal logger

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11710
| License       | MIT
| Doc PR        | -

Is it really necessary to check for `\pL` and `\pN` *only*?
If the check is only for utf-8, then `'//u'` is enough.
Also, this is strange we looking at the condition just after this one (see full file): because of this very test, we are sure that this is utf8 string, but just after, we still do a mb_detect_encoding?