Strings compile fix due to core package change

[petardz]

Description

Changed Strings class package due to change in core, to fix compile issues

Issues Resolved

[List any issues this PR will resolve]

Check List

• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov]

Codecov Report

Merging #680 (ebcd049) into main (f922857) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##               main     #680   +/-   ##
=========================================
  Coverage     61.84%   61.84%           
  Complexity      114      114           
=========================================
  Files            73       73           
  Lines          2495     2495           
  Branches        266      266           
=========================================
  Hits           1543     1543           
  Misses          775      775           
  Partials        177      177           

Flag	Coverage Δ
opensearch-notifications	61.84% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...ensearch/notifications/spi/model/MessageContent.kt	0.00% <ø> (ø)
...ifications/spi/model/destination/SesDestination.kt	0.00% <ø> (ø)
...fications/spi/model/destination/SmtpDestination.kt	0.00% <ø> (ø)
...earch/notifications/spi/utils/ValidationHelpers.kt	43.33% <ø> (ø)
...arch/notifications/core/utils/ValidationHelpers.kt	28.00% <ø> (ø)

[opensearch-trigger-bot]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-2.x 2.x
# Navigate to the new working tree
cd .worktrees/backport-2.x
# Create a new branch
git switch --create backport/backport-680-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 36f1fcb6d7552729e7640adb82b4f65b87349132
# Push it to GitHub
git push --set-upstream origin backport/backport-680-to-2.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-680-to-2.x.