Windows CI: fix YAML break — replace SFX-config heredoc with printf

The previous commit's bash heredoc for the 7-Zip SFX config:
  cat > sfx-config.txt <<'SFXCFG'
  ;!@Install@!UTF-8!
  ...
  SFXCFG
…had its body at the left margin (since heredoc lines are taken
literally). But the surrounding YAML used `run: |` which requires
every line to be indented more than the `run:` key. The unindented
heredoc body broke out of the block scalar — Gitea Actions
rejected the workflow with "could not find expected ':'" at the
;!@Install line.

Switch to a single `printf '...' > sfx-config.txt` line that fits
cleanly inside the YAML block. Same on-disk file content, no YAML
indentation conflict.

.github/workflows/build-windows.yml

@@ -355,14 +355,9 @@ jobs:
           # 2. SFX config — runtime behavior of the wrapper .exe.
           # RunProgram is what fires after extraction. HashWallet is the
           # BINARY_NAME baked into windows/CMakeLists.txt.
-          cat > sfx-config.txt <<'SFXCFG'
-;!@Install@!UTF-8!
-Title="Hash Bags"
-BeginPrompt=""
-Progress="yes"
-RunProgram="HashWallet.exe"
-;!@InstallEnd@!
-SFXCFG
+          # Using printf instead of a heredoc because bash heredoc bodies
+          # have no indentation and break out of YAML's `run: |` block.
+          printf ';!@Install@!UTF-8!\nTitle="Hash Bags"\nBeginPrompt=""\nProgress="yes"\nRunProgram="HashWallet.exe"\n;!@InstallEnd@!\n' > sfx-config.txt
 
           # 3. Concatenate SFX module + config + payload → final .exe.
           # Identical to the Windows "copy /b a + b + c" idiom; cat works