Pull Request for Issue #30928 .

Summary of Changes

This pull request (PR) adds the necessary SQL statements to delete the obsolete record for plg_authentication_gmail in the extension table to the update SQL scripts.

I order to not add again a new update SQL script, I've decided to modify the existing script 4.0.0-2020-09-27.sql, which hasn't been released yet and so can be modified, as we don't support updates between nightlies.

If a new Beta or whatever else release of J4 will be made before this PR will be merged, I'll have to move the new statement to a new update SQL script then.

If my other PR #30945 which updates the same SQL scripts is merged before this one, I have to solve conflicts here before this one can be merged.

Testing Instructions

Test 1: Reproduce the issue

1. Update a clean installation (i.e. no 3rd party extensions) of current 3.10-dev or latest 3.10 nightly or 3.10-alpha2 to the latest 4.0 nightly, using the following custom URL for Live Update or the following update package for Upload & Update:

• Custom update URL = https://update.joomla.org/core/nightlies/next_major_list.xml
• Update package = https://developer.joomla.org/nightlies/Joomla_4.0.0-beta5-dev-Development-Update_Package.zip

2. After successful update, go to the "System - Manage - Plugins" and check if there is an authentication plugin with name "plg_authentication_gmail".
   Result: The plugin exists.
3. Go to "System - Manage - Extensions" and search for "plg_authentication_gmail".
   Result: The plugin exists.
4. Try to uninstall the plugin.
   Result: Error "Call to a member function attributes() on null", see also section "Actual result BEFORE applying this Pull Request" below.

Test 2: Verify that this PR fixes the issue when updating from 3.10-dev

Repeat the previous test "Test 1", but this time use the update package of latest 4.0 nightly plus the fix of this PR included.

• Custom update URL = https://ci.joomla.org/artifacts/joomla/joomla-cms/4.0-dev/30941/downloads/36178/pr_list.xml
• Update package = https://ci.joomla.org/artifacts/joomla/joomla-cms/4.0-dev/30941/downloads/36178/Joomla_4.0.0-beta5-dev+pr.30941-Development-Update_Package.zip

Result: The plugin doesn't exists, see also section "Expected result AFTER applying this Pull Request" below.

Test 3: Verify that this PR fixes the issue when updating a 4.0 Beta 4

Repeat the previous test "Test 2", but this time don't start from a 3.10 installation.

Start from an installation of 4.0 Beta 4 instead.

It has to be 4.0 Beta 4 and not current 4.0-dev or latest 4.0 nighty.

Result: The plugin doesn't exists, see also section "Expected result AFTER applying this Pull Request" below.

Actual result BEFORE applying this Pull Request

After an update from 3.10 to 4, there is still an authentication plugin with name "plg_authentication_gmail" in the extensions table in database and so in the list of plugins in backend.

Trying to uninstall that results in an error "Call to a member function attributes() on null".

Expected result AFTER applying this Pull Request

After an update from 3.10 to 4, there is no authentication plugin with name "plg_authentication_gmail" in the extensions table in database and in the list of plugins in backend.

After update from a 4 Beta version which had the issue to a future 4 version which contains the fix from this PR, the obsolete authentication plugin "plg_authentication_gmail" will be deleted.

Documentation Changes Required

None.