[Tooling] Don't fail lint on strings not in base language

[AliSoftware]

Why

Last beta lane failed on ios_lint_localizations because a string was removed from the codebase in the code-frozen release/* branch in #25022.

This caused the linter to complain about this for all locales:

`reader.blog.search.loading.title` was unexpected, as it is not present in the base locale.

How

• Added fail_on_strings_not_in_base_language: false parameter to ios_lint_translations
• Run the download_localized_strings lane, to ensure we download the latest translations from GlotPress, especially to get the changes on postTags.addTag, postTags.searchOrAdd.placeholder and postTags.selectionEmpty that apparently had a placeholder added in their English copy since initially introduced (which is quite dangerous as it can lead to crashes if not all locales are translated with the new copy in time, which is the main reason for the localization linting to be in place) and were otherwise (rightfully, this time) generating linter errors.

Testing instructions

Run bundle exec fastlane lint_localizations from this branch and validate it does not error anymore about keys missing in the base locale.

[dangermattic]

	2 Warnings
⚠️	This PR is larger than 500 lines of changes. Please consider splitting it into smaller PRs for easier and faster reviews.
⚠️	This PR is assigned to the milestone 26.5 ❄️. The due date for this milestone has already passed. Please assign it to a milestone with a later deadline or check whether the release for this milestone has already been finished.

Generated by 🚫 Danger

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[oguzkocer]

Works as described

[wpmobilebot]

📲 You can test the changes from this Pull Request in WordPress by scanning the QR code below to install the corresponding build.

	App Name	WordPress
	Configuration	Release-Alpha
	Build Number	29992
	Version	PR #25030
	Bundle ID	org.wordpress.alpha
	Commit	878d877
	Installation URL	10fuk8eer9be8

Automatticians: You can use our internal self-serve MC tool to give yourself access to those builds if needed.

[wpmobilebot]

📲 You can test the changes from this Pull Request in Jetpack by scanning the QR code below to install the corresponding build.

	App Name	Jetpack
	Configuration	Release-Alpha
	Build Number	29992
	Version	PR #25030
	Bundle ID	com.jetpack.alpha
	Commit	878d877
	Installation URL	2t2rjijl48el8

Automatticians: You can use our internal self-serve MC tool to give yourself access to those builds if needed.