fetchHistoryAcrossLinks does not work for branched packages

[dcermak]

The following code fails:

await fetchHistoryAcrossLinks(this.con, { apiUrl, name: "rubygem-nokogiri", projectName: "Virtualization:vagrant"});

with an assertion:

AssertionError [ERR_ASSERTION]: Got an invalid history back, expected HEAD of linked package (devel:languages:ruby:extensions/rubygem-nokogiri) to be at undefined or 30cd3513bb3264cdf0350a5c398faf09 but got a356e1cb541160288f9465fc03c57617

This is caused by us using linkrev=base to fetch the expanded revisions in

open-build-service-api/src/history.ts

Line 215 in c108991

`/source/${pkg.projectName}/${pkg.name}?expand=1&linkrev=base&rev=${rev.revisionHash}`

This works mostly, but it breaks if we have a package that has been branched, as then the following assertion fails:

open-build-service-api/src/history.ts

Line 487 in c108991

assert(

This might be possible to fix by inserting the expanded revisions with and without linkrev=base into the commit cache.