Fix release metadata updates in workflows

[erseco]

Summary

• Fix reading $plugin->version in the editor release watcher.
• Replace fragile shell/sed substitutions for $plugin->version and $plugin->release with explicit Python updates.
• Apply the same fix to the post-release transition back to dev.

Cause

The workflow used double-quoted sed expressions containing \$plugin. Shell expansion removed the intended literal $, so version.php was not modified. The subsequent release validation therefore still saw $plugin->release = 'dev' and failed.

This is the failure observed in Actions run 31183409991 while preparing v4.0.3.

Expected result

After this PR is merged, rerunning Check Editor Releases should create the Prepare plugin release v4.0.3 PR with real release metadata, and the post-release step should later return main to a new monotonic development version safely.

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Moodle Playground Preview

The changes in this pull request can be previewed and tested using a Moodle Playground instance.

ℹ️ The eXeLearning editor is fetched from the shared release and unpacked into the plugin when the playground boots, so the first load may take a few extra seconds. ELPX upload, viewer and preview work normally.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.31%. Comparing base (6327499) to head (b4a2f08).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #119   +/-   ##
=========================================
  Coverage     92.31%   92.31%           
  Complexity      824      824           
=========================================
  Files            51       51           
  Lines          3734     3734           
=========================================
  Hits           3447     3447           
  Misses          287      287           

Flag	Coverage Δ
javascript	94.11% <ø> (ø)
php	92.23% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
PHP (server-side)	92.23% <ø> (ø)
JavaScript (SCORM tracker)	94.11% <ø> (ø)

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