Silence warning from MySQL::Error object in test

When running Active Record MySQL test, this warning is printed in the
console:

    warning: instance variable errno not initialized

It turns out that this is a warning from `mysql` gem in MySQL::Error
object. However, since the `mysql` gem is no longer maintained, and
there won't be a newer version, it make sense for us to just silence
this warning to make the output cleaner.

Remove unused WorkshopsController class in redirect_test.

Closes #19866

[ci skip]

[ci skip] Description inside Signed and Encrypted CookieJars added

commit a88875ac6abaa4d8116b42af8cd71189ce3d44d3
Author: Siddharth Bhatore <sbhatore95@gmail.com>
Date:   Thu Apr 23 12:26:08 2015 +0530

    [ci skip] Update doc fix cookies

commit f175eaa7a21db898fc6c66334f770831028f9d00
Author: Siddharth Bhatore <sbhatore95@gmail.com>
Date:   Mon Apr 20 12:58:04 2015 +0530

    Description inside Signed and Encrypted CookieJars added

Fix missing index when using timestamps with index

Fix CSS formatting in welcome#index.html.erb

Fix a minor grammatical issue in the doc [ci skip]

[ci skip] Add, clean up docs in ActionDispatch ActionDispatch middleware

That seems to be a bug, but as we don't actually care about the
precision for our test, we'll just give it a bit longer.

[Matthew Draper & Cristian Bica]

Support for versions of SQLite less than 3 was removed in #6011 as part
of the Rails 4.0 release. Therefore there is no need to have support for
it in the `rails dbconsole` command anymore.

Fix find_each options [ci skip]

We only want to support adapters that we officially support through the
entire framework so it is better to not ask patches for adapters that
we may not support

Improve ActiveSupport::TimeWithZone conversion to YAML

Fix formatting of scaffold css

Clearify that alias_method_chain is deprecated

Previously when converting AS::TimeWithZone to YAML it would be output
as a UTC timestamp. Whilst this preserves the time information accurately
it loses the timezone information. This commit changes that so that it is
saved along with the time information. It also provides nicer encoding of
AS::TimeZone instances themselves which previously embedded all of the
data from the TZInfo records.

Fixes #9183.

Make strptime behave more like parse when components are missing and
share behavior between the two methods.

This makes it easier to parse user-inputted times as from a given time zone.

This was not clear on the API documentation that the method was
deprecated in a982a42d.

Silence warning from requiring mathn

[ci skip] UpgradeLegacySignedCookieJar Doc fix

Running Action View test case currently printing out this warning:

    lib/mathn.rb is deprecated

This should silence the warning since we really want to require this
file in this test.

MRI compatible code for ActiveSupport::Testing::Isolation::Subprocess

Add newlines between divs in form scaffolding

Improve the Contributing to Rails Guide [skip ci]

Activemode::Dirty attributes query methods consistency before and after saving.

`ActiveModel::Dirty#[attr_name]_previous_change` to improve access
to recorded changes after the model has been saved.

It makes the dirty-attributes query methods consistent before and after
saving.

update Ruby required version in Getting Started guide [ci skip]