action: recognise .iso images in the release assets manifest

The manifest generator's EXTS table lacked any iso entry, so an
image-output-iso build (e.g. the Armbian SDK) produced a .iso.xz that was
never matched - it got no <image>.assets.json and so never appeared in the
aggregated armbian-images.json. Add iso.xz / iso.zst / iso rows (image_format
"iso") and an "iso" -> "iso" FORMAT_SUFFIX so the friendly redirect variant
is disambiguated from the raw image (…_minimal-iso). Handles both the
compressed and the uncompressed ISO forms.

Verified with the embedded generator against a fake image dir: the .iso.xz
now yields a manifest with file_extension "iso.xz", and raw .img + .iso for
the same board coexist as separate entries with distinct redi URLs.

Signed-off-by: Igor Pecovnik <igor@armbian.com>

action.yml

@@ -298,6 +298,9 @@ runs:
             ("hyperv.zip.xz",  "hyperv.zip"),
             ("hyperv.zip.zst", "hyperv.zip"),
             ("hyperv.zip",     "hyperv.zip"),
+            ("iso.xz",         "iso"),
+            ("iso.zst",        "iso"),
+            ("iso",            "iso"),
             ("img.xz",         "img"),
             ("img.zst",        "img"),
             ("img",            "img"),
@@ -306,7 +309,7 @@ runs:
         # image_format -> redi_url variant suffix (canonical generator
         # appends "-qcow2" / "-hyperv" to the friendly redirect path so a
         # board can serve multiple formats at distinct URLs).
-        FORMAT_SUFFIX = {"img.qcow2": "qcow2", "img.vhdx": "vhdx", "hyperv.zip": "hyperv"}
+        FORMAT_SUFFIX = {"img.qcow2": "qcow2", "img.vhdx": "vhdx", "hyperv.zip": "hyperv", "iso": "iso"}
 
         # Filename: Armbian[-unofficial]_{version}_{Board}_{distro}_{branch}_{kernel}[_{variant[.app]}]
         # Variant token is optional (some legacy / hand-crafted builds omit it).