Fix YAML compilation error in multiline run blocks

[Copilot]

The workflow compiler generated invalid YAML when creating prompt steps. The run: key was written as a single-line value, but subsequent heredoc content at the same indentation level was parsed as new mapping keys, causing go-yaml validation to fail with "value is not allowed in this context."

Changes

• pkg/workflow/compiler_yaml.go: Use YAML multiline literal format (run: |) for prompt creation steps
  • Changed line 211 from run: bash ... to run: | with bash command on next indented line
  • Ensures heredoc content is properly parsed as part of the run block value

Before

run: bash /tmp/gh-aw/actions/create_prompt_first.sh
  cat << 'PROMPT_EOF' > "$GH_AW_PROMPT"
  # Content here...
  PROMPT_EOF

After

run: |
  bash /tmp/gh-aw/actions/create_prompt_first.sh
  cat << 'PROMPT_EOF' > "$GH_AW_PROMPT"
  # Content here...
  PROMPT_EOF

All 123 workflow lock files regenerated with corrected YAML syntax.

Original prompt

Fix the compilation of workflows. it generates invalid yaml.

@pelikhan ➜ /workspaces/gh-aw (main) $ ./gh-aw compile smoke-copilot
✓ .github/workflows/smoke-copilot.md (317.2 KB)
generated lock file is not valid YAML: [2104:11] value is not allowed in this context. map key-value is pre-defined
2102 | # Smoke Test: Copilot Engine Validation
2103 |

2104 | IMPORTANT: Keep all outputs extremely short and concise. Use single-line responses where possible. No verbose explanations.
^
2106 | ## Test Requirements
2107 |
✗ Compiled 1 workflow(s): 1 error(s), 0 warning(s)
✗ Failed workflows:

• /workspaces/gh-aw/.github/workflows/smoke-copilot.md (1 error)
  ✗ generated lock file is not valid YAML: [2104:11] value is not allowed in this context. map key-value is pre-defined
  2102 | # Smoke Test: Copilot Engine Validation
  2103 |

2104 | IMPORTANT: Keep all outputs extremely short and concise. Use single-line responses where possible. No verbose explanations.
^
2106 | ## Test Requirements
2107 |

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