CI: Make input variables to cache actions mandatory

Cache variables should always be explicit, and we already pass them in
everywhere. This makes it easier to spot errors in our cache setup.

.github/actions/cache-restore/action.yml

@@ -6,27 +6,21 @@ inputs:
   os:
     description: 'Operating System to restore caches for'
     required: true
-    default: 'Linux'
   arch:
     description: 'Target Architecture to restore caches for'
-    required: false
-    default: 'x86_64'
+    required: true
   toolchain:
     description: 'Toolchain to restore caches for (GNU or Clang)'
-    required: false
-    default: 'GNU'
+    required: true
   cache_key_extra:
     description: 'Code coverage setting, ON or OFF, or debug setting, ALL or NORMAL'
-    required: false
-    default: 'OFF'
+    required: true
   ccache_path:
     description: 'Path to the ccache directory'
-    required: false
-    default: ''
+    required: true
   vcpkg_cache_path:
     description: 'Path to vcpkg binary cache'
-    required: false
-    default: ''
+    required: true
 
 outputs:
   ccache_primary_key:

.github/actions/cache-save/action.yml

@@ -5,24 +5,19 @@ author: 'Andrew Kaster <akaster@serenityos.org>'
 inputs:
   arch:
     description: 'Target Architecture to restore caches for'
-    required: false
-    default: 'x86_64'
+    required: true
   ccache_path:
     description: 'Path to the ccache directory'
-    required: false
-    default: ''
+    required: true
   ccache_primary_key:
     description: 'Primary ccache key'
-    required: false
-    default: ''
+    required: true
   vcpkg_cache_path:
     description: 'Path to the vcpkg binary cache directory'
-    required: false
-    default: ''
+    required: true
   vcpkg_cache_primary_key:
     description: 'Primary vcpkg binary cache key'
-    required: false
-    default: ''
+    required: true
 
 runs:
   using: 'composite'