Fixed running Rust unit tests in CI

[lslezak]

Problem

• The CI tests actually do not run the Rust unit tests, only the documentation tests.

Solution

• The --doc tarpaulin option means "Test only this library's documentation" so the unit tests were not executed
• Use also the --all-targets option which means "Test all targets (excluding doctests)"
• The --all option is deprecated alias for the --workspace option, use --workspace directly
• Symlink all langtable data files (the complete directory)

Testing

• Tested manually, all unit tests are executed

Notes

• The CI failure here is expected and shows that the unit tests are really executed