Bump actions/cache from 3 to 4 (#30)

Bumps [actions/cache](https://github.com/actions/cache) from 3 to 4.
- [Release notes](https://github.com/actions/cache/releases)
- [Changelog](https://github.com/actions/cache/blob/main/RELEASES.md)
- [Commits](actions/cache@v3...v4)

---
updated-dependencies:
- dependency-name: actions/cache
  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

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-20.04
     steps:
     - uses: actions/checkout@master
-    - uses: actions/cache@v3
+    - uses: actions/cache@v4
       with:
         path: ~/.local/share/virtualenvs
         key: ${{ runner.os }}-poetry-${{ hashFiles('poetry.lock') }}
@@ -33,7 +33,7 @@ jobs:
     runs-on: ubuntu-20.04
     steps:
     - uses: actions/checkout@master
-    - uses: actions/cache@v3
+    - uses: actions/cache@v4
       with:
         path: ~/.local/share/virtualenvs
         key: ${{ runner.os }}-poetry-${{ hashFiles('poetry.lock') }}