gha: don't double-quote board/maintainer filter values

[iav]

Summary

The chunk template userpatches/gha/chunks/050.single_header.yaml — used by
recreate-matrix.yml to (re)generate all complete-artifact-matrix-*.yml
workflows — wraps the inputs.board and inputs.maintainer values in
literal double quotes inside single-quoted strings:

FILTERS="${{ github.event.inputs.targetsFilterInclude }}"

if [ -z "${FILTERS}" ] && [ "${{ ... .board }}" != "all" ] && [ -n "${{ ... .board }}" ]; then
    FILTERS='"BOARD:${{ github.event.inputs.board }}"'
fi

if [ -z "${FILTERS}" ] && [ "${{ ... .maintainer }}" != "all" ] && [ -n "${{ ... .board }}" ]; then
    FILTERS='"BOARD_MAINTAINERS:${{ github.event.inputs.maintainer }}"'
fi
...
TARGETS_FILTER_INCLUDE="${FILTERS}" \

bash single quotes preserve content verbatim, so $FILTERS ends up as
the literal 8-character string "BOARD:helios64" (quotes included). Bash
then substitutes that into the command line as-is, and compile.sh
receives a TARGETS_FILTER_INCLUDE value whose quotes are part of the
string.

lib/tools/info/targets-compositor.py splits the filter on : and ends
up with key='"BOARD' / value='helios64"' — no board in inventory
matches that key, and the run fails at Prepare Info JSON and Matrices:

No invocations left after filtering '{'key': '"BOARD', 'value': 'helios64"'}'!
ERROR: command failed with error code 2

Reproduction

Trigger Build Standard Support Images (admin) from Actions and pick
any concrete board from the board: combobox (e.g. helios64), leave
everything else at defaults → Run workflow.

Fresh failures (both on the same board:helios64 input):

• run 25888743879 → https://paste.armbian.com/kiluqafuvo
• run 25890339566 → https://paste.armbian.com/ujasuwuqin

Fix

Drop the wrapping double quotes — single quotes already preserve the
value verbatim, no escaping is needed:

- FILTERS='"BOARD:${{ github.event.inputs.board }}"'
+ FILTERS='BOARD:${{ github.event.inputs.board }}'
- FILTERS='"BOARD_MAINTAINERS:${{ github.event.inputs.maintainer }}"'
+ FILTERS='BOARD_MAINTAINERS:${{ github.event.inputs.maintainer }}'

Two-line change, single source file. The five generated
complete-artifact-matrix-*.yml files will pick up the fix on the next
recreate-matrix.yml run (manual dispatch or the existing cron: 00 5 * * *
schedule).

Notes

• Not a recent regression — last commit touching the source chunk is
  0460037 (2026-03-15, "Update actions"); it did not change these lines.
  The bug has been latent since the board: / maintainer: combobox
  inputs were introduced. Most users probably feed targetsFilterInclude
  directly and never hit this path.
• Workaround until merged: leave board=all (and maintainer=all) in the
  form, and set targetsFilterInclude=BOARD:<board> directly — that
  input flows into FILTERS via line 318 (FILTERS="${{ ... .targetsFilterInclude }}"), which is not wrapped in extra quotes.

Test plan

• After merge, dispatch recreate-matrix.yml (or wait for cron).
• Confirm regenerated .github/workflows/complete-artifact-matrix-*.yml
  files contain FILTERS='BOARD:${{ ... }}' (no inner quotes).
• Re-dispatch Build Standard Support Images (admin) with
  board=helios64, confirm the Prepare Info JSON and Matrices step
  passes and the matrix is non-empty.