CI: meson 1.6.0 has been released. add older versions to CI matrix

Author: dnicolodi

.github/workflows/tests.yml

@@ -88,6 +88,12 @@ jobs:
           - os: ubuntu-latest
             python: '3.12'
             meson: '~=1.3'
+          - os: ubuntu-latest
+            python: '3.12'
+            meson: '~=1.4'
+          - os: ubuntu-latest
+            python: '3.12'
+            meson: '~=1.5'
           # Test with Meson master branch.
           - os: ubuntu-latest
             python: '3.12'