CI: github: switch development builds back to ubuntu-latest

It was changed by 50cf89a ("CI: bump development builds explicitely to
Ubuntu 24.04"), but it was just a matter of cleaning the cache.

Switch development builds back to ubuntu-latest (and ubuntu-latest-arm)
and update stable branches to ubuntu-26.04.

diff --git a/.github/matrix.py b/.github/matrix.py
index 12b38df20b0b0304a55810fb2ae938127a6b1c34..1d452d02d6c4a48c178d5517ebcfc14ca5093e97 100755 (executable)
--- a/.github/matrix.py
+++ b/.github/matrix.py
@@ -174,13 +174,13 @@ def main(ref_name):
     # Ubuntu
 
     if is_stable:
-        os = "ubuntu-24.04"         # stable branch
-        os_arm = "ubuntu-24.04-arm" # stable branch
-        os_i686 = "ubuntu-24.04"    # stable branch
+        os = "ubuntu-26.04"         # stable branch
+        os_arm = "ubuntu-26.04-arm" # stable branch
+        os_i686 = "ubuntu-26.04"    # stable branch
     else:
-        os = "ubuntu-24.04"         # development branch
-        os_arm = "ubuntu-24.04-arm" # development branch
-        os_i686 = "ubuntu-24.04"    # development branch
+        os = "ubuntu-latest"         # development branch
+        os_arm = "ubuntu-latest-arm" # development branch
+        os_i686 = "ubuntu-latest"    # development branch
 
     TARGET = "linux-glibc"
     for CC in ["gcc", "clang"]: