Bump swift and change GH action

Author: craigwrong

.github/workflows/docs.yml

@@ -23,9 +23,15 @@ jobs:
         with:
           repository: swift-bitcoin/swift-bitcoin
       - name: Install Swift
-        uses: sersoft-gmbh/swifty-linux-action@v3
+        # uses: sersoft-gmbh/swifty-linux-action@v3
+        # with:
+            # release-version: 6.1.2
+        uses: vapor/swiftly-action@v0.2
         with:
-            release-version: 6.1
+            toolchain: 6.1.2
+        # uses: swift-actions/setup-swift@v2
+        # with:
+            # swift-version: 6.1
       - name: Build docs
         run: tools/generate-docs.sh
         env: