Update GHA actions (#40)

Old actions were blocking build

Author: haydenmc

.github/workflows/linux-x64.yml

@@ -13,19 +13,19 @@ jobs:
 
     steps:
     - name: Setup .NET
-      uses: actions/setup-dotnet@v3
+      uses: actions/setup-dotnet@v4
       with:
         dotnet-version: 8.0.x
     - name: Clone repository
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
     - name: Restore dependencies
       run: dotnet restore src/Theorem.sln
     - name: Build
       run: dotnet build --no-restore src/Theorem.sln
     - name: Publish
       run: dotnet publish -c Release -r linux-x64 --self-contained=true -p:PublishReadyToRun=true -o publish/Theorem src/Theorem/Theorem.csproj
     - name: Upload Artifact
-      uses: actions/upload-artifact@v2
+      uses: actions/upload-artifact@v4
       with:
         name: Theorem
         path: publish/Theorem