[OpenJDK 2D-Dev] RFR: 8204122: Update harfbuzz.md

[Phil Race]

Bug: https://bugs.openjdk.java.net/browse/JDK-8204122

I pushed harfbuzz 1.7.6 without updating the version in the legal file.
The diff is trivial so I am including inline here :

--- a/src/java.desktop/share/legal/harfbuzz.md
+++ b/src/java.desktop/share/legal/harfbuzz.md
@@ -1,4 +1,4 @@
-## Harfbuzz v1.7.1
+## Harfbuzz v1.7.6


I checked the rest of the text in that file does not need to change.

-phil.