fix(isMobilePhone): correct de-LU regex to allow all valid mobile prefixes

The de-LU (Luxembourg) mobile phone regex incorrectly required the
third digit to be '1' (pattern: 6\d1), rejecting valid numbers like
+352628123456 or +352678123456.

Changed (6\d1) to (6\d{2}) to accept all Luxembourg mobile numbers
starting with 6 followed by any two digits.

Added test cases covering previously rejected valid prefixes (628, 661,
671, 691) and an additional invalid case.

Closes #1727

Author: tommyhgunz14

src/lib/isMobilePhone.js

@@ -31,7 +31,7 @@ const phones = {
   'de-DE': /^((\+49|0)1)(5[0-25-9]\d|6([23]|0\d?)|7([0-57-9]|6\d))\d{7,9}$/,
   'de-AT': /^(\+43|0)\d{1,4}\d{3,12}$/,
   'de-CH': /^(\+41|0)([1-9])\d{1,9}$/,
-  'de-LU': /^(\+352)?((6\d1)\d{6})$/,
+  'de-LU': /^(\+352)?((6\d{2})\d{6})$/,
   'dv-MV': /^(\+?960)?(7[2-9]|9[1-9])\d{5}$/,
   'el-GR': /^(\+?30|0)?6(8[5-9]|9(?![26])[0-9])\d{7}$/,
   'el-CY': /^(\+?357?)?(9(9|7|6|5|4)\d{6})$/,

test/validators.test.js

@@ -10659,6 +10659,13 @@ describe('Validators', () => {
         valid: [
           '601123456',
           '+352601123456',
+          '+352621123456',
+          '+352628123456',
+          '+352661123456',
+          '+352671234567',
+          '+352691234567',
+          '628123456',
+          '691234567',
         ],
         invalid: [
           'NaN',
@@ -10669,6 +10676,7 @@ describe('Validators', () => {
           '+112039812',
           '+352703123456',
           '1234',
+          '+352512345678',
         ],
       },
       {