Fix flaky `build-runtimes-polkavm` CI job (#6893)

The timeout was too low which made the job not finish in time sometimes:

Hence:
- Bumping the timeout to 60 minutes which is in line with other jobs
which are building substantial parts of the repo.
- Roll all the runtime builds into a single cargo invocation so that it
aborts after the first failure. It also allows for more parallel
compiling.