The IRS page dates March 19, 2019, and I can find no record of Congress passing a law to continue those credits.
They don't have to pass a law to extend the plug-in credit. They would have to pass a law to repeal it.
I see
Credit for certain nonbusiness energy property
...
Form 8936, Instructions, Qualified Plug-in Electric Drive Motor Vehicle Credit
It is the nonbusiness energy property credit that has expired, not the plug-in credit. The IRS site is listing forms related to the nonbusiness energy property credit.
So why is form 8936 listed as one of the related forms for the Non-business Energy Property Credit? I guess while we are asking that we can also ask why is Pub 972, Child Tax Credit also listed as being related to the nonbusiness energy property credit also. Well that takes us into the thickest part of the weeds in the IRS jungle.
There are two different credits going on:
Residential Energy Efficient Property Credit (REEP)
Non-business Energy Property Credit
REEP is about solar electric, solar water heaters, etc. This credit had expired but was extended and continues.
The Non-business Energy Property Credit is primarily about improvements such as heat pumps, energy efficient windows, etc. This credit expired after 2017 and has so far not been extended.
Both credits are claimed on form 5965. REEP is entered into Part 1 of the form, Non-business Energy Property in Part 2 (on the 2018 form Part 2 is listed as "Reserved for Future Use").
In the instructions for the REEP part of form 5965 it lists some other credits that the taxpayer might be also claiming which can affect the amount of the REEP credit. They are:
• Credit for the elderly or the disabled.
• Adoption credit.
• Mortgage interest credit.
• District of Columbia first-time homebuyer credit.
• Alternative motor vehicle credit.
• Qualified plug-in electric vehicle credit.
• Qualified plug-in electric drive motor vehicle credit
The amount of these credits is entered into a worksheet that calculates the amount of REEP credit allowed.
However looking at prior years when nonbusiness energy property credit was included these limitations never had anything to do with the nonbusiness energy property credit, only the REEP credit. In prior years the nonbusiness energy property credit was only limited by the credit for the elderly or the disabled.
So personally I think it is a mistake on the IRS site that form 8936 Qualified Plug-in Electric Drive Motor Vehicle Credit is listed as one of the affected forms for the nonbusiness energy property credit. I suspect someone just lazily listed everything related to form 5965. But even if it had been related it would just mean that the amount of the nonbusiness energy property credit might be reduced if someone is also taking the plug-in credit that same year. It would not mean that the plug-in credit has also expired.
But that is based solely on having recently stayed at a Holiday Inn Express. You will need to consult with a tax advisor if you want to be sure.