Print missing repos in downstream check script

[VenelinMartinov]

fixes #1816

Hit it during #1854

It now prints links for the repos which don't have PRs for the commit at all:

FAILURE https://github.com/pulumi/pulumi-auth0/pull/493
FAILURE https://github.com/pulumi/pulumi-oci/pull/431
MISSING https://github.com/pulumi/pulumi-opsgenie/actions/workflows/upgrade-bridge.yml
MISSING https://github.com/pulumi/pulumi-splunk/actions/workflows/upgrade-bridge.yml
MISSING https://github.com/pulumi/pulumi-libvirt/actions/workflows/upgrade-bridge.yml
MISSING https://github.com/pulumi/pulumi-minio/actions/workflows/upgrade-bridge.yml
MISSING https://github.com/pulumi/pulumi-kafka/actions/workflows/upgrade-bridge.yml
MISSING https://github.com/pulumi/pulumi-aws/actions/workflows/upgrade-bridge.yml
MISSING https://github.com/pulumi/pulumi-onelogin/actions/workflows/upgrade-bridge.yml
MISSING https://github.com/pulumi/pulumi-cloudamqp/actions/workflows/upgrade-bridge.yml
MISSING https://github.com/pulumi/pulumi-rabbitmq/actions/workflows/upgrade-bridge.yml
MISSING https://github.com/pulumi/pulumi-newrelic/actions/workflows/upgrade-bridge.yml
MISSING https://github.com/pulumi/pulumi-dnsimple/actions/workflows/upgrade-bridge.yml
MISSING https://github.com/pulumi/pulumi-nomad/actions/workflows/upgrade-bridge.yml
MISSING https://github.com/pulumi/pulumi-mailgun/actions/workflows/upgrade-bridge.yml
MISSING https://github.com/pulumi/pulumi-mysql/actions/workflows/upgrade-bridge.yml
MISSING https://github.com/pulumi/pulumi-sumologic/actions/workflows/upgrade-bridge.yml
MISSING https://github.com/pulumi/pulumi-vsphere/actions/workflows/upgrade-bridge.yml
MISSING https://github.com/pulumi/pulumi-keycloak/actions/workflows/upgrade-bridge.yml
MISSING https://github.com/pulumi/pulumi-slack/actions/workflows/upgrade-bridge.yml
MISSING https://github.com/pulumi/pulumi-vault/actions/workflows/upgrade-bridge.yml

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.47%. Comparing base (17265a0) to head (b3f6758).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1869      +/-   ##
==========================================
- Coverage   60.48%   60.47%   -0.02%     
==========================================
  Files         310      310              
  Lines       42835    42835              
==========================================
- Hits        25909    25903       -6     
- Misses      15453    15458       +5     
- Partials     1473     1474       +1     

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