Move from stickler to flake8 github actions

.github/workflows/flake8-linter-matcher.json

@@ -0,0 +1,17 @@
+{
+    "problemMatcher": [
+        {
+            "owner": "flake8-linter-error",
+            "severity": "error",
+            "pattern": [
+                {
+                    "regexp": "^([^:]+):(\\d+):(\\d+):\\s+([EWCNF]\\d+\\s+.+)$",
+                    "file": 1,
+                    "line": 2,
+                    "column": 3,
+                    "message": 4
+                }
+            ]
+        }
+    ]
+}

.github/workflows/flake8.yml

@@ -0,0 +1,27 @@
+name: Flake8 Linter
+on:
+  pull_request:
+jobs:
+  flake8-linter:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout source
+        uses: actions/checkout@v3
+      - name: Install Python 3.10
+        uses: actions/setup-python@v4
+        with:
+          python-version: '3.10'
+      - name: Install Flake8 5.0.4 linter
+        run: pip install flake8==5.0.4  # use this version for --diff option
+      - name: Setup Flake8 output matcher for PR annotations
+        run: echo '::add-matcher::.github/workflows/flake8-linter-matcher.json'
+      - name: Fetch pull request target branch
+        run: |
+          git remote add upstream https://github.com/eqcorrscan/EQcorrscan.git
+          git fetch upstream $GITHUB_BASE_REF
+      - name: Run Flake8 linter
+        run: git diff upstream/$GITHUB_BASE_REF HEAD | flake8
+          --exclude eqcorrscan/doc
+          --ignore W605,W504,W503
+          --max-line-length 80
+          --diff