Fix typos in bt709 and bt2020 test image filenames

These test images were added in commit
ea65e680:
https://crrev.com/c/2321307

Bug: 1108626
Change-Id: I35f7b58ab9b38d308744513c77b617e271fcd47b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2365220Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Wan-Teh Chang <wtc@google.com>
Cr-Commit-Position: refs/heads/master@{#799888}

third_party/blink/web_tests/images/resources/avif/README.md

@@ -45,7 +45,7 @@ These are all generated from red.png with the appropriate avifenc command line:
 
 BT.709:
 ```
-avifenc -r f -d  8 -y 444 -s 0 --nclx 1/1/1 red.png red-full-range-bt709-pq-444-8bpc.avif
+avifenc -r f -d  8 -y 444 -s 0 --nclx 1/1/1 red.png red-full-range-bt709-444-8bpc.avif
 ```
 
 PQ:
@@ -56,8 +56,8 @@ avifenc -r f -d 10 -y 444 -s 0 --nclx 9/16/9 red.png red-full-range-bt2020-pq-44
 
 HLG:
 ```
-avifenc -r f -d 10 -y 444 -s 0 --nclx 9/18/9 red.png red-full-range-bt2020-pq-444-10bpc.avif
-avifenc -r f -d 10 -y 444 -s 0 --nclx 9/18/9 red.png red-full-range-bt2020-pq-444-12bpc.avif
+avifenc -r f -d 10 -y 444 -s 0 --nclx 9/18/9 red.png red-full-range-bt2020-hlg-444-10bpc.avif
+avifenc -r f -d 10 -y 444 -s 0 --nclx 9/18/9 red.png red-full-range-bt2020-hlg-444-12bpc.avif
 ```
 
 ### silver-full-range-srgb-420-8bpc.avif