Correct de_fuehrerschein docstring to match the actual pattern scope (#2138)

The class docstring gives "B0" (Berlin) as an example of a
Behördenkürzel and lists `B012345678A` in the Examples line, but the
regex `[A-Z]{2}\d{8}[A-Z0-9]` requires both leading characters to be
letters, so `B012345678A` never matches. The test file's docstring is
the authoritative one — it explicitly notes that single-letter Kfz
codes are used in 2-letter authority forms (e.g. `BO`, `KN`) and that
`B0`-style single-letter-plus-digit combinations are out of scope, and
`test_when_all_de_fuehrerschein_numbers_then_succeed` asserts
`B12345678A` is rejected.

Update the class docstring to match the tests: replace the `"B0"
Berlin` example with `"BO" Bochum`, add a short clarification about
single-letter Kfz codes, and change the misleading `B012345678A`
Examples entry to `BO12345678A`.

Co-authored-by: Sharon Hart <sharonh.dev@gmail.com>

Author: jichaowang02-lang

presidio-analyzer/presidio_analyzer/predefined_recognizers/country_specific/germany/de_fuehrerschein_recognizer.py

@@ -13,9 +13,13 @@ class DeFuehrerscheinRecognizer(PatternRecognizer):
     via FeV reform), the number follows a fixed 11-character structure:
 
         Pos 1–2:   Behördenkürzel – 2 uppercase letters identifying the issuing
-                   Fahrerlaubnisbehörde (derived from the Kfz-Zulassungskürzel of
-                   the issuing Kreis/Stadt, e.g. "B0" Berlin, "MU" München,
-                   "HH" Hamburg, "KO" Koblenz)
+                   Fahrerlaubnisbehörde (derived from the Kfz-Zulassungskürzel
+                   of the issuing Kreis/Stadt, e.g. "MU" München, "HH" Hamburg,
+                   "KO" Koblenz, "BO" Bochum).  Single-letter Kfz codes such
+                   as "B" (Berlin) or "K" (Köln) are used in combination as
+                   2-letter authority codes here (e.g. "BO", "KN"); pure
+                   single-letter + digit forms like "B0" are out of scope for
+                   this strict pattern (see tests/test_de_fuehrerschein_recognizer.py).
         Pos 3–5:   Behördennummer – 3-digit authority code within the Bundesland
                    (assigned by the Kraftfahrt-Bundesamt, KBA)
         Pos 6–10:  Laufende Nummer – 5-digit sequential issue number
@@ -27,7 +31,7 @@ class DeFuehrerscheinRecognizer(PatternRecognizer):
     EU standard: Annex I to Directive 2006/126/EC (Field 5).
     Data protection: DSGVO Art. 4 Nr. 1 (personenbezogene Daten), BDSG.
 
-    Examples (fictitious): B012345678A, MU12345678B, HH98765432C
+    Examples (fictitious): BO12345678A, MU12345678B, HH98765432C
 
     Scope note: Pre-2013 German driving licenses (pink folded card, laminated
     card) used locally defined, non-standardized number formats and remain