Set correct permissions of `/tmp` dir during GSC build

[dimakuv]

Description of the changes

The original app image may have changed the permissions of /tmp dir. At the same time, correct permissions are required for installation of packages during GSC build. This commit adds explicit chmod 1777 /tmp.

Fixes #193.

How to test this PR?

Looks like a reproducer would be like this:

FROM debian:12
RUN chmod 1777 /tmp
USER ${non_root_uid}:${non_root_gid}

But I haven't tested really.

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This change is