Index: .github/workflows/build.yml
===================================================================
diff -u -r0129b8b89f86bcd559a2d1e296db8c32086770ec -rb7b00a04d72dc35037a80d36acf3316709c1c469
--- .github/workflows/build.yml	(.../build.yml)	(revision 0129b8b89f86bcd559a2d1e296db8c32086770ec)
+++ .github/workflows/build.yml	(.../build.yml)	(revision b7b00a04d72dc35037a80d36acf3316709c1c469)
@@ -84,6 +84,14 @@
             compiler: gcc-10
             tcltag: core-8-7-a5
             experimental: [false]
+          - os: ubuntu-latest
+            compiler: gcc-10
+            tcltag: core-8-6-13-rc
+            experimental: [true]
+          - os: macos-latest
+            compiler: gcc-11
+            tcltag: core-8-6-13-rc
+            experimental: [true]
     defaults:
       run:
         shell: bash