ci: add s390x runner (using QEMU), for the tests in builtin, os, and encoding.binary

[spytheman]

• ci: add a small s390x testing job (a big endian system)
• add a base_image: tag
• install make and gcc first
• add githubToken: and shell: tags
• remove file ./v command, since file is not installed
• install file, coreutils and binutils as well
• use --no-install-recommends for the apt-get command
• remove --no-install-recommends
• test also vlib/os and vlib/encoding/binary
• os: fix os_test.c.v for QEMU s390x
• cleanup

[huly-for-github]

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