Maintenance: Update dependency icalendar to v2.10.3

Gemfile.lock

@@ -300,8 +300,9 @@ GEM
     httpclient (2.8.3)
     i18n (1.14.6)
       concurrent-ruby (~> 1.0)
-    icalendar (2.10.2)
+    icalendar (2.10.3)
       ice_cube (~> 0.16)
+      ostruct
     icalendar-recurrence (1.2.0)
       icalendar (~> 2.0)
       ice_cube (~> 0.16)
@@ -443,6 +444,7 @@ GEM
     openssl (3.2.0)
     openssl-signature_algorithm (1.3.0)
       openssl (> 2.0)
+    ostruct (0.1.0)
     overcommit (0.64.0)
       childprocess (>= 0.6.3, < 6)
       iniparse (~> 1.4)