Drupal 9 support

ops!

Just add the new line, so it remains compatible with versions less than 8.8

+++ b/zircon.info.yml
@@ -4,7 +4,7 @@ base theme: classy
+core_version_requirement: '^8 || ^9'

Created a merge request that kept the core: 8.x for compatibility below 8.7.7.

Thanks @all!

While I don't work on the D8/D9 version of Zircon at all, I know that this simple change can help people make the move to D9, so I merged the suggested change.

Thanks @MegaChriz!

Hi,
I am running on Drupal 8.9.19 with the old Zircon version 8x1.0-rc1. In order to upgrade to the latest D9 version of Drupal 9.0.14, I was trying to first upgrade the old Zircon version on D8.9.19, and got the following errors.

1. First, I was upgrading the Zircon, with the latest (on 17Sep 21 - Zircon 8x1-dev) updated version on the Drupal website. But the following error message appeared --- --- Module admin_toolbar_search has an entry in the system.schema key/value storage, but is not installed. More information about this error --- ---.

2. Then, I added the patch code as suggested in the weblink (https://www.drupal.org/files/issues/2020-06-24/d9-compatibility-3154623....) in the Zircon.info.yml - But while updating the site crashed. Maybe I have added the Patch wrongly - This is how I added it.
------------------------------------------------------------------------------------------
name: Zircon
type: theme
diff --git a/zircon.info.yml b/zircon.info.yml
index 9d3fc19..6f7f20c 100644
--- a/zircon.info.yml
+++ b/zircon.info.yml
@@ -4,7 +4,7 @@ base theme: classy
description: 'A flexible, recolorable theme with many regions and a responsive, mobile-first layout.'
package: Core
# version: 8.1.3
-core: 8.x
+core_version_requirement: '^8 || ^9'
libraries:
- zircon/global-styling
regions:
------------------------------------------------------------------------------------
Shall appreciate your comments.

I thought of clarifying the MAIN ISSUE OF ZIRCON 8x1-DEV UPGRADE WITH DRUPAL VERSION of 8.9.19. Actually, the upgrade is going through, but while opening the site - the site seems to work, BUT THE WEBSITE loses its FORMATING with random pages.