chore(ci): correctly compute $DIST_TAG in the deploy-code CI job

Previously, the `DIST_TAG` environment variable was failing to be
computed correctly in the `deploy-code` CI job, because it relied on the
non-existent `node` executable. It worked with the default executor
(which includes `node`), but not with the `cloud-sdk` executor used in
`deploy-code`, resulting in the following error:

```sh
./.circleci/env.sh: line 59: node: command not found
DIST_TAG=
```

You can see an example failure in the "Set up environment" step logs in
https://app.circleci.com/pipelines/github/angular/angular.js/
170/workflows/32fcacf9-c89b-4020-b3eb-15debe18bb67/jobs/1793

This commit fixes it by computing `$DIST_TAG` using unix tools (`cat`,
`grep`, `sed`) that _are_ available on the docker images of all
executors.

Closes angular#17067

.circleci/env.sh

@@ -56,7 +56,9 @@ setPublicVar SAUCE_READY_FILE_TIMEOUT 120
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 # Define additional environment variables
 ####################################################################################################
-setPublicVar DIST_TAG $( node --print "require('./package.json').distTag" )
+
+# NOTE: Make sure the tools used to compute this are available in all executors in `config.yml`.
+setPublicVar DIST_TAG $( cat package.json | grep distTag | sed -E 's/^\s*"distTag"\s*:\s*"([^"]+)"\s*,\s*$/\1/' )
 
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