Merge pull request #61 from RobWalt/update-ci

Update github actions versions which caused the following warnings in the github actions tab:

```
The following actions uses Node.js version which is deprecated and will be forced to run on node20: actions/checkout@v3, actions/cache@v3. For more info: https://github.blog/changelog/202...
```

Author: RobWalt

.github/workflows/ci.yml

@@ -15,8 +15,8 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 60
     steps:
-      - uses: actions/checkout@v3
-      - uses: actions/cache@v3
+      - uses: actions/checkout@v4
+      - uses: actions/cache@v4
         with:
           path: |
             ~/.cargo/bin/
@@ -38,8 +38,8 @@ jobs:
   clippy:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
-      - uses: actions/cache@v3
+      - uses: actions/checkout@v4
+      - uses: actions/cache@v4
         with:
           # cache the build files! see: https://github.com/actions/cache
           path: |
@@ -61,8 +61,8 @@ jobs:
   rustfmt:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
-      - uses: actions/cache@v3
+      - uses: actions/checkout@v4
+      - uses: actions/cache@v4
         with:
           # cache the build files! see: https://github.com/actions/cache
           path: |