GHA: set version via "git describe"

* for this to work, we need to set "fetch-depth",
  in order to check out all tags

.github/workflows/main.yml

@@ -14,6 +14,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
+      with:
+        fetch-depth: 0
     - name: Setup .NET Core
       uses: actions/setup-dotnet@v4
       with:
@@ -23,14 +25,16 @@ jobs:
     - name: Install dependencies
       run: dotnet restore src/GeoJSON.Net.sln
     - name: Build
-      run: dotnet build src/GeoJSON.Net.sln --configuration Release --no-restore
+      run: dotnet build src/GeoJSON.Net.sln -c Release --no-restore -p:Version=$(git describe --tags)
     - name: Test
       run: dotnet test src/GeoJSON.Net.sln --no-restore --verbosity normal
 
   winBuild:
     runs-on: windows-latest
     steps:
     - uses: actions/checkout@v2
+      with:
+        fetch-depth: 0
     - name: Setup .NET Core
       uses: actions/setup-dotnet@v4
       with:
@@ -40,6 +44,6 @@ jobs:
     - name: Install dependencies
       run: dotnet restore src/GeoJSON.Net.sln
     - name: Build
-      run: dotnet build src/GeoJSON.Net.sln --configuration Release --no-restore
+      run: dotnet build src/GeoJSON.Net.sln -c Release --no-restore -p:Version=$(git describe --tags)
     - name: Test
       run: dotnet test src/GeoJSON.Net.sln --no-restore --verbosity normal