fix: include Package.swift in cache key to prevent stale caches

The cache key was only using Package.resolved hash, which meant when
Package.swift dependencies changed, the cache wasn't invalidated.

This caused Ubuntu Swift 6.2 release builds to use stale cached artifacts
from before the HTMLElementTypesFoundation dependency was added.

Now cache key includes both:
- Package.swift (dependency declarations)
- Package.resolved (resolved versions)

This ensures cache is invalidated when dependencies change.

Author: coenttb

.github/workflows/ci.yml

@@ -31,7 +31,7 @@ jobs:
         uses: actions/cache@v4
         with:
           path: .build
-          key: ${{ runner.os }}-spm-${{ hashFiles('Package.resolved') }}
+          key: ${{ runner.os }}-spm-${{ hashFiles('Package.swift', 'Package.resolved') }}
           restore-keys: |
             ${{ runner.os }}-spm-
 
@@ -51,7 +51,7 @@ jobs:
         uses: actions/cache@v4
         with:
           path: .build
-          key: ${{ runner.os }}-spm-${{ hashFiles('Package.resolved') }}
+          key: ${{ runner.os }}-spm-${{ hashFiles('Package.swift', 'Package.resolved') }}
           restore-keys: ${{ runner.os }}-spm-
 
       # Note: swift test builds automatically in release mode
@@ -71,7 +71,7 @@ jobs:
         uses: actions/cache@v4
         with:
           path: .build
-          key: ${{ runner.os }}-swift60-spm-${{ hashFiles('Package.resolved') }}
+          key: ${{ runner.os }}-swift60-spm-${{ hashFiles('Package.swift', 'Package.resolved') }}
           restore-keys: ${{ runner.os }}-swift60-spm-
 
       # Note: swift test builds automatically