fix: improve typespec-python regeneration workflow

- Fix README template step to create README.md in all package dirs,
  not just replace existing ones. This ensures newly generated packages
  (e.g. typeddict variants) always get a README.
- Add target_branch input to workflow_dispatch so manual runs can push
  to a separate branch without affecting the main baseline.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: iscai-msft

.github/workflows/typespec-python-regenerate.yml

@@ -16,6 +16,10 @@ on:
         description: "Either 'main' (microsoft/typespec@main) or a microsoft/typespec pull request URL (e.g. https://github.com/microsoft/typespec/pull/1234). The PR's head repo + SHA will be checked out."
         required: false
         default: "main"
+      target_branch:
+        description: "Branch to push regenerated tests to. Defaults to 'typespec-python-generated-tests'."
+        required: false
+        default: "typespec-python-generated-tests"
 
 permissions:
   contents: write
@@ -148,19 +152,23 @@ jobs:
             echo "::error::Template README not found at $TEMPLATE"
             exit 1
           fi
-          # Replace every README.md under generated/ with the template, except:
-          #   - the top-level generated/README.md
-          #   - anything under generated/template/ (the template itself and any
-          #     future siblings)
-          find "$TARGET" -type f -name README.md \
-            ! -path "$TARGET/README.md" \
-            ! -path "$TARGET/template/*" \
-            -print -exec cp -f "$TEMPLATE" {} \;
+          # Place a README.md in every package directory under azure/ and
+          # unbranded/ (top-level subdirectories only). This ensures newly
+          # generated packages get a README, not just pre-existing ones.
+          for flavor in azure unbranded; do
+            flavor_dir="$TARGET/$flavor"
+            [ -d "$flavor_dir" ] || continue
+            for pkg_dir in "$flavor_dir"/*/; do
+              [ -d "$pkg_dir" ] || continue
+              cp -f "$TEMPLATE" "$pkg_dir/README.md"
+              echo "  $pkg_dir/README.md"
+            done
+          done
 
       - name: Commit and push to dedicated branch
         run: |
           set -euo pipefail
-          BRANCH="typespec-python-generated-tests"
+          BRANCH="${{ github.event.inputs.target_branch || 'typespec-python-generated-tests' }}"
           git config user.name "github-actions[bot]"
           git config user.email "github-actions[bot]@users.noreply.github.com"