variable substitutions ${canonicalUrl} cutting off urls at a comma

### Description

"$DEFAULT(${canonicalUrl}, notSet)" doesn't seem to report the URLs correctly in amp-analytics. It looks like for some reason the reported urls get cut of at the comma (,)

### Reproduction Steps

e.g. https://amp.tvspielfilm.de/news/tv/tatort-neugeboren-neues-bremer-team-macht-so-weiter-wie-das-alte-aufgehoert-hat,10428438,ApplicationArticle.html

look for rt.tvspielfilm.de/collect in the network console to confirm that the reported canonical url is
https://www.tvspielfilm.de/news/tv/tatort-neugeboren-neues-bremer-team-macht-so-weiter-wie-das-alte-aufgehoert-hat
rather than
https://www.tvspielfilm.de/news/tv/tatort-neugeboren-neues-bremer-team-macht-so-weiter-wie-das-alte-aufgehoert-hat,10428438,ApplicationArticle.html

### Relevant Logs

_No response_

### Browser(s) Affected

Chrome

### AMP Version Affected

2105072136000

Start in the amp-analytics handling of the "$DEFAULT(${canonicalUrl}, notSet)" substitution and reproduce the issue with the URL in the report. Inspect the network request to rt.tvspielfilm.de/collect; done means the canonical URL remains complete, including the comma and following path text.

Written by the indexing model from the issue text.