Use quotes for matrix values

Signed-off-by: Daniel Kastl <[email protected]>

Author: dkastl

.github/workflows/test-postgis.yml

@@ -25,9 +25,9 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        redmine_version: [5.0-stable, 5.1-stable, master]
-        ruby_version: [3.0, 3.1, 3.2]
-        db_version: [12-3.0, 15-3.3]
+        redmine_version: ['5.0-stable', '5.1-stable', 'master']
+        ruby_version: ['3.0', '3.1', '3.2']
+        db_version: ['12-3.0', '15-3.3']
         include:
           - system_test: true
             redmine_version: 5.1-stable