gh-114240: Skip verifying pip SBOM entry against PyPI if offline outside CI

[sethmlarson]

Closes #114240 This PR implements my proposal from this comment: #114240 (comment)

We decide whether to exit(1) or skip based on the presence of the CI environment variable. If there's another existing standard that we're using for this sort of behavior happy to use that instead.

@befeleme Would this work for your use-case?

• Issue: Don't run regen-sbom in regen-all - it requires internet access #114240

[befeleme]

In theory, probably yes. I can't verify, since as we don't ship Python's bundled pip (#114244) the script fails a bit sooner for us:

    if len(pip_wheels) != 1:
        print("Zero or multiple pip wheels detected in 'Lib/ensurepip/_bundled'")
        sys.exit(1)

[sethmlarson]

I've closed this in favor of #114450, all of these requirements were pretty tightly linked so combined into one PR.