fix: downgrade gittools/actions to v3 for GitVersion 5.x compatibility

gittools/actions@v4 requires GitVersion >=6.1.0, but the workflow
uses versionSpec 5.x. v3 supports the full 5.x-6.x range.

Author: JerrettDavis

.github/workflows/ci.yml

@@ -152,13 +152,13 @@ jobs:
         run: git fetch --prune --tags
 
       - name: Install GitVersion
-        uses: gittools/actions/gitversion/setup@v4
+        uses: gittools/actions/gitversion/setup@v3
         with:
           versionSpec: '5.x'
 
       - name: Run GitVersion
         id: gitversion
-        uses: gittools/actions/gitversion/execute@v4
+        uses: gittools/actions/gitversion/execute@v3
 
       - name: Set version env vars
         run: |