CmdPal: Update Back button tooltip with shortcut information (#40718)

## Summary of the Pull Request

The tooltip for the "Back" button has been modified to include the
keyboard shortcut "Back (Alt + Left arrow)" instead of the previous text
"Back".

<img width="283" height="182" alt="image"
src="https://github.com/user-attachments/assets/3ff0bddc-30fd-4bbb-a0c0-3b68c0060640"
/>


## PR Checklist

- [ ] **Closes:** #xxx
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

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## Detailed Description of the Pull Request / Additional comments

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## Validation Steps Performed

src/modules/cmdpal/Microsoft.CmdPal.UI/Strings/en-us/Resources.resw

@@ -411,7 +411,7 @@ Right-click to remove the key combination, thereby deactivating the shortcut.</v
     <value>Back</value>
   </data>
   <data name="BackButton.[using:Microsoft.UI.Xaml.Controls]ToolTipService.ToolTip" xml:space="preserve">
-    <value>Back</value>
+    <value>Back (Alt + Left arrow)</value>
   </data>
   <data name="MoreCommandsButton.[using:Microsoft.UI.Xaml.Automation]AutomationProperties.Name" xml:space="preserve">
     <value>More</value>