Update release-calendar.md

Author: fdevans

docs/history/release-calendar.md

@@ -9,6 +9,7 @@ Upgrade instructions [can be found here](/upgrading/index.md).
 
 | Release Version                          | Release Date         | Enterprise Support Status |
 |------------------------------------------|----------------------|---------------------------|
+| [5.18.0](/history/5_x/version-5.18.0.md)   | December 16th, 2025   | Supported |
 | [5.17.0](/history/5_x/version-5.17.0.md)   | November 3rd, 2025   | Supported |
 | [5.16.0](/history/5_x/version-5.16.0.md)   | October 6th, 2025   | Supported |
 | [5.15.0](/history/5_x/version-5.15.0.md)   | September 2nd, 2025   | Supported |
@@ -21,7 +22,6 @@ Upgrade instructions [can be found here](/upgrading/index.md).
 | [5.10.1](/history/5_x/version-5.10.1.md)   | April 15th, 2025   | Supported |
 | [5.10.0](/history/5_x/version-5.10.0.md)   | March 14th, 2025   | Supported |
 | [5.9.0](/history/5_x/version-5.9.0.md)   | February 5th, 2025   | Supported |
-| [5.8.0](/history/5_x/version-5.8.0.md)   | December 5th, 2024   | Supported |
 
 ::: warning
 Any versions not listed here are now out of support.  We encourage everyone on older versions to update to a currently supported version.