Upgrade CI Ubuntu (#128)

* Dependabot: Automatically upgrade GitHub Actions

* GitHub Actions: Update runner Ubuntu version and actions versions

Author: elopez

.github/dependabot.yml

@@ -0,0 +1,6 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "daily"

.github/workflows/ci.yml

@@ -12,17 +12,17 @@ on:
 
 jobs:
   tests:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-22.04
     strategy:
       fail-fast: false
       matrix:
         type: ["slither", "manticore"]
     steps:
-    - uses: actions/checkout@v1
-    - name: Set up Python 3.6
-      uses: actions/setup-python@v1
+    - uses: actions/checkout@v3
+    - name: Set up Python 3.8
+      uses: actions/setup-python@v4
       with:
-        python-version: 3.6
+        python-version: 3.8
     - name: Install dependencies
       run: |
         sudo wget -O /usr/bin/solc https://github.com/ethereum/solidity/releases/download/v0.5.11/solc-static-linux

.github/workflows/echidna.yml

@@ -14,7 +14,7 @@ jobs:
   tests:
     name: ${{ matrix.name }}
     continue-on-error: ${{ matrix.flaky == true }}
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-22.04
     strategy:
       fail-fast: false
       matrix: