tests: don't do so many internet requests

[Luap99]

Each network request increases the chances flakes, tests should always avoid making external requests as much as possible.
Example failures observed in podman: https://api.cirrus-ci.com/v1/artifact/task/6035732734672896/html/bud-podman-fedora-42-root-host-sqlite.log.html

# STEP 6/7: ADD https://github.com/containers/buildah/blob/main/README.md /tmp/
# Error: building at STEP "ADD https://github.com/containers/buildah/blob/main/README.md /tmp/": reading "https://github.com/containers/buildah/blob/main/README.md": invalid response status 429

Unless there is some strong reason I suggest these tests should setup their own local websever to serve these contents so they don't have to reach out to servers we don't control.

[Luap99]

Link https://github.blog/changelog/2025-05-08-updated-rate-limits-for-unauthenticated-requests/

I think we really cannot use so many direct github requests here as this will keep causing flakes. (I see quite a lot on podman buildah bud tests)
@nalind @flouthoc Any reason that the tests are using github? Can we setup our own local web server on localhost the serves static content in the tests instead?
I know there are some tests for git clone and the likes those could maybe be converted to a local git repo setup?

This might be something @timcoding1988 could work on.