Fix YAML: indent heredoc Python code to block-scalar level

Python heredoc lines at column 0 were parsed by YAML as content
outside the block scalar. Indent all heredoc lines by 10 spaces
(the run: block indent level) so YAML includes them; YAML then
strips the leading 10 spaces before passing to bash.

Also switch from shell variable substitution inside heredoc to
os.environ so the heredoc can use a quoted delimiter ('PYEOF').

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

Author: mballance

.github/workflows/fvutils-weekly-report.yaml

@@ -97,28 +97,31 @@ jobs:
         run: |
           WEEK_END=$(date -u '+%d %b %Y')
 
-          # Build the JSON payload with Python to avoid shell quoting issues
-          python3 - << PYEOF
-import json, os
-activity = open('/tmp/activity.md').read()
-week_end = "$WEEK_END"
-model    = "$MODEL"
-prompt = (
-    "You are a technical writer for an open-source verification tools project.\n\n"
-    f"Below is raw weekly activity (commits, PRs, issues) from the fvutils GitHub org "
-    f"for the week ending {week_end}.\n\n"
-    + activity +
-    "\n\nWrite a concise weekly news item suitable for the project website. "
-    "Include: a short overall summary paragraph, then a per-repo highlights section "
-    "using bullet points, and a brief \"What's next\" closing line. "
-    "Be factual, avoid hype, use past tense for completed work."
-)
-payload = {"model": model, "messages": [{"role": "user", "content": prompt}],
-           "max_tokens": 600, "temperature": 0.4}
-with open('/tmp/request.json', 'w') as f:
-    json.dump(payload, f)
-print("Request JSON written.")
-PYEOF
+          # Build the JSON payload with Python to avoid shell quoting issues.
+          # All heredoc lines are indented 10 spaces so YAML includes them in the
+          # block scalar; YAML strips the 10-space prefix before passing to bash.
+          export WEEK_END MODEL
+          python3 - << 'PYEOF'
+          import json, os
+          activity = open('/tmp/activity.md').read()
+          week_end = os.environ['WEEK_END']
+          model    = os.environ['MODEL']
+          prompt = (
+              "You are a technical writer for an open-source verification tools project.\n\n"
+              f"Below is raw weekly activity (commits, PRs, issues) from the fvutils GitHub org "
+              f"for the week ending {week_end}.\n\n"
+              + activity
+              + "\n\nWrite a concise weekly news item suitable for the project website. "
+              "Include: a short overall summary paragraph, then a per-repo highlights section "
+              "using bullet points, and a brief \"What's next\" closing line. "
+              "Be factual, avoid hype, use past tense for completed work."
+          )
+          payload = {"model": model, "messages": [{"role": "user", "content": prompt}],
+                     "max_tokens": 600, "temperature": 0.4}
+          with open('/tmp/request.json', 'w') as f:
+              json.dump(payload, f)
+          print("Request JSON written.")
+          PYEOF
 
           gh api -X POST "/models/$MODEL/chat/completions" \
             --input /tmp/request.json \