chore: validate plurals in strings.xml | FC-55

[OmarIthawi]

Plurals are failing the transifex import. I've fixed them manually in #341, but more are coming. Therefore a GitHub Actions is needed.

Testing

Example failure:

• https://github.com/openedx/openedx-app-android/actions/runs/9610916922/job/26508405063#step:5:33

core/src/main/res/values/strings.xml:        <item quantity="zero">Due %1$d days ago</item>
core/src/main/res/values/strings.xml:        <item quantity="two">Due %1$d days ago</item>
make: *** [Makefile:15: validate_english_plurals] Error 1
core/src/main/res/values/strings.xml:        <item quantity="few">Due %1$d days ago</item>
core/src/main/res/values/strings.xml:        <item quantity="many">Due %1$d days ago</item>
core/src/main/res/values/strings.xml:        <item quantity="zero">Due in %1$d days</item>
core/src/main/res/values/strings.xml:        <item quantity="two">Due in %1$d days</item>
core/src/main/res/values/strings.xml:        <item quantity="few">Due in %1$d days</item>
core/src/main/res/values/strings.xml:        <item quantity="many">Due in %1$d days</item>
course/src/main/res/values/strings.xml:        <item quantity="zero">%1$s of %2$s  assignments complete</item>
course/src/main/res/values/strings.xml:        <item quantity="two">%1$s of %2$s  assignments complete</item>
course/src/main/res/values/strings.xml:        <item quantity="few">%1$s of %2$s  assignments complete</item>
course/src/main/res/values/strings.xml:        <item quantity="many">%1$s of %2$s  assignments complete</item>
dashboard/src/main/res/values/strings.xml:        <item quantity="zero">%1$d Past Due Assignments</item>
dashboard/src/main/res/values/strings.xml:        <item quantity="two">%1$d Past Due Assignments</item>
dashboard/src/main/res/values/strings.xml:        <item quantity="few">%1$d Past Due Assignments</item>
dashboard/src/main/res/values/strings.xml:        <item quantity="many">%1$d Past Due Assignments</item>

Error: Found invalid plurals in the files listed above.
       Please only use 'one' and 'other' in English strings.xml files,
       otherwise Transifex fails to parse them.

The second commit fixes those failures and the CI passes correctly.

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[OmarIthawi]

Thanks @volodymyr-chekyrta for the quick review. Kindly merge that the new fix commit has been pushed.

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