Use the matrix identifier to name the "Check Certificates" workflow jobs

When no name is provided for a matrix job, the workflow job is named according to the contents of
`jobs[].<job_id>.strategy.matrix[]`. That can result in some fairly cryptic job names when the matrix contains a complex
data structure as is the case here. We already have a string to uniquely identify each certificate to humans, which is
exactly what the `jobs[].<job_id>.name` property does for jobs, so it will be an improvement to name the jobs according
to that identifier.

.github/workflows/check-certificates.yml

@@ -20,6 +20,7 @@ env:
 
 jobs:
   check-certificates:
+    name: ${{ matrix.certificate.identifier }}
     # Only run when the workflow will have access to the certificate secrets.
     if: >
       (github.event_name != 'pull_request' && github.repository == 'arduino/arduino-create-agent') ||