Bump actions/cache from 4 to 5 (#78)

Bumps [actions/cache](https://github.com/actions/cache) from 4 to 5.
- [Release notes](https://github.com/actions/cache/releases)
- [Changelog](https://github.com/actions/cache/blob/main/RELEASES.md)
- [Commits](actions/cache@v4...v5)

---
updated-dependencies:
- dependency-name: actions/cache
  dependency-version: '5'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/main.yml

@@ -57,15 +57,15 @@ jobs:
 
       - name: Stan build caching
         # note: not quite working since we use a development branch of Stan
-        uses: actions/cache@v4
+        uses: actions/cache@v5
         id: stan-cache
         with:
           path: ./stan/
           key: ${{ runner.os }}-stan-${{ hashFiles('stan/src/stan/version.hpp') }}-v${{ env.CACHE_VERSION }}
 
       # we use the cache here to build the Stan models once for multiple interfaces
       - name: Set up test model cache
-        uses: actions/cache@v4
+        uses: actions/cache@v5
         id: test-models
         with:
           path: ./test_models/
@@ -95,14 +95,14 @@ jobs:
           python-version: ${{ matrix.python-version }}
 
       - name: Restore Stan
-        uses: actions/cache@v4
+        uses: actions/cache@v5
         id: stan-cache
         with:
           path: ./stan/
           key: ${{ runner.os }}-stan-${{ hashFiles('stan/src/stan/version.hpp') }}-v${{ env.CACHE_VERSION }}
 
       - name: Restore built models
-        uses: actions/cache@v4
+        uses: actions/cache@v5
         id: test-models
         with:
           path: ./test_models/
@@ -156,13 +156,13 @@ jobs:
             any::posterior
 
       - name: Restore Stan
-        uses: actions/cache@v4
+        uses: actions/cache@v5
         with:
           path: ./stan/
           key: ${{ runner.os }}-stan-${{ hashFiles('stan/src/stan/version.hpp') }}-v${{ env.CACHE_VERSION }}
 
       - name: Restore built models
-        uses: actions/cache@v4
+        uses: actions/cache@v5
         id: test-models
         with:
           path: ./test_models/
@@ -205,14 +205,14 @@ jobs:
           channel: ${{ matrix.julia-version }}
 
       - name: Restore Stan
-        uses: actions/cache@v4
+        uses: actions/cache@v5
         id: stan-cache
         with:
           path: ./stan/
           key: ${{ runner.os }}-stan-${{ hashFiles('stan/src/stan/version.hpp') }}-v${{ env.CACHE_VERSION }}
 
       - name: Restore built models
-        uses: actions/cache@v4
+        uses: actions/cache@v5
         id: test-models
         with:
           path: ./test_models/