ci: transform tarball to one top level directory

[eshattow]

Transform path name with GNU tar and tilde search-replace delimiter from list at https://libgit2.org/docs/reference/main/tag/git_tag_create as that delimiter would never appear in git ref name.

[eshattow]

Note an apparent a bug in GNU tar yields a directory listing output that is not column-aligned. I tried several variations of tar invocation, for example mv dist foo && tar cf foo.tar.gz foo style, but the outcome is the same when within GitHub CI/CD environment; I cannot reproduce it on my desktop host. I have sent an email message to bug-tar mailing list asking about that. The extracted content appears to be consistent so I won't delay this fix.

Update: This wandering column output appears when the ownership information is runner/runner as the length of text is just so to make it obvious that tar doesn't know all the sizes of files as it is processing the file listing beforehand. It's an expected behavior I never notice in several decades' time when my own usernames are shorter or longer than this.