regen.sh - Fix warning on PHP 8.2 (strtr() - Passing null)

After running regen, toward the end of the process, there are some warnings like:

```
Generating Membership
Generating MembershipPayment
Generating MembershipLog

Deprecated: strtr(): Passing null to parameter #1 ($string) of type string is deprecated in /home/totten/bknix/build/dmaster/web/sites/all/modules/civicrm/CRM/Core/CodeGen/GenerateData.php on line 1563

Call Stack:
    0.0035     423192   1. {main}() /home/totten/bknix/build/dmaster/web/sites/all/modules/civicrm/sql/GenerateData.php:0
    1.0962   56966984   2. CRM_Core_CodeGen_GenerateData->generateAll() /home/totten/bknix/build/dmaster/web/sites/all/modules/civicrm/sql/GenerateData.php:86
    2.6564  102240512   3. CRM_Core_CodeGen_GenerateData->generate($itemName = 'MembershipLog') /home/totten/bknix/build/dmaster/web/sites/all/modules/civicrm/CRM/Core/CodeGen/GenerateData.php:84
    2.6564  102240560   4. CRM_Core_CodeGen_GenerateData->addMembershipLog() /home/totten/bknix/build/dmaster/web/sites/all/modules/civicrm/CRM/Core/CodeGen/GenerateData.php:113
    2.6592  102261720   5. CRM_Core_CodeGen_GenerateData::repairDate($date = NULL) /home/totten/bknix/build/dmaster/web/sites/all/modules/civicrm/CRM/Core/CodeGen/GenerateData.php:1580
   30.7495  102266384   6. strtr($string = NULL, $from = ['-' => '', ':' => '', ' ' => '']) /home/totten/bknix/build/dmaster/web/sites/all/modules/civicrm/CRM/Core/CodeGen/GenerateData.php:1563

Deprecated: strtr(): Passing null to parameter #1 ($string) of type string is deprecated in /home/totten/bknix/build/dmaster/web/sites/all/modules/civicrm/CRM/Core/CodeGen/GenerateData.php on line 1563

Call Stack:
    0.0035     423192   1. {main}() /home/totten/bknix/build/dmaster/web/sites/all/modules/civicrm/sql/GenerateData.php:0
    1.0962   56966984   2. CRM_Core_CodeGen_GenerateData->generateAll() /home/totten/bknix/build/dmaster/web/sites/all/modules/civicrm/sql/GenerateData.php:86
    2.6564  102240512   3. CRM_Core_CodeGen_GenerateData->generate($itemName = 'MembershipLog') /home/totten/bknix/build/dmaster/web/sites/all/modules/civicrm/CRM/Core/CodeGen/GenerateData.php:84
    2.6564  102240560   4. CRM_Core_CodeGen_GenerateData->addMembershipLog() /home/totten/bknix/build/dmaster/web/sites/all/modules/civicrm/CRM/Core/CodeGen/GenerateData.php:113
   30.7583  102263704   5. CRM_Core_CodeGen_GenerateData::repairDate($date = NULL) /home/totten/bknix/build/dmaster/web/sites/all/modules/civicrm/CRM/Core/CodeGen/GenerateData.php:1580
   30.7583  102263704   6. strtr($string = NULL, $from = ['-' => '', ':' => '', ' ' => '']) /home/totten/bknix/build/dmaster/web/sites/all/modules/civicrm/CRM/Core/CodeGen/GenerateData.php:1563

Generating PCP
Generating SoftContribution
Generating Pledge
Generating PledgePayment
```

CRM/Core/CodeGen/GenerateData.php

@@ -1556,6 +1556,9 @@ private function addMembership() {
    * @return string
    */
   public static function repairDate($date) {
+    if ($date === NULL) {
+      return '';
+    }
     $dropArray = ['-' => '', ':' => '', ' ' => ''];
     return strtr($date, $dropArray);
   }