Add parse workflow

.gitattributes

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+# Don't export certain files via `git archive` (e.g. via "Download ZIP")
+.gitattributes export-ignore
+.github export-ignore

.github/workflows/ci.yaml

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+name: CI
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    types: [opened, synchronize]
+
+concurrency:
+  group: ${{ github.ref }}-${{ github.workflow }}-${{ github.event_name }}
+  cancel-in-progress: true
+
+jobs:
+  test-parse:
+    name: Data Files
+    runs-on: windows-2022
+    env:
+      CONTINUOUS: EndlessSky-win64-continuous.zip
+      GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+    steps:
+    - name: Download latest continuous
+      run: gh release download -R endless-sky/endless-sky continuous -p ${{ env.CONTINUOUS }}
+    - name: Extract and prepare continuous
+      run: |
+        Expand-Archive ${{ env.CONTINUOUS }} -DestinationPath endless-sky -Force
+        cd .\endless-sky
+        mkdir plugins
+        cd .\plugins
+        mkdir all-content-plugin
+    - uses: actions/checkout@v4
+      with:
+        path: '.\endless-sky\plugins\all-content-plugin'
+    - name: Parse Datafiles
+      run: "'.\\endless-sky\\Endless Sky.exe' -p"
+      shell: bash