fix: only seach ts files for scopes

[bkleiner]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngneat/transloco/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

Fix scopes extraction in cases where webpack emits a folder.

[X] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

It appears in some situations webpack emits folders in the files array.
The files array is passed directly to the the updateScopesMap function.
This leads webpack to crash when it's trying to be read.

Error: EISDIR: illegal operation on a directory, read

Issue Number: N/A

What is the new behavior?

Only *.ts files are passed to the updateScopesMap function as files.

Does this PR introduce a breaking change?

[ ] Yes
[X] No

Other information

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