Mention Bug Fix in release notes

GNU Privacy Guard was patched to no longer [warn about an "invalid
format"](git-for-windows/git#2743) when
private and public keys are stored separately.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

ReleaseNotes.md

@@ -47,6 +47,7 @@ This package contains software from a number of other projects including Bash, z
 * The credential helper selector (used as default credential helper in the Portable Git) [now persists the users choice correctly again](https://github.com/git-for-windows/git/issues/2776).
 * The full command-lines of MSYS2 processes (such as `cp.exe`) spawned from Git's Bash [can now be seen in `sysmon`, `wmic` etc](https://github.com/git-for-windows/git/issues/2756) by default.
 * A [bug](https://github.com/git-for-windows/git/issues/2738) preventing Unicode characters from being used in the window title of Git Bash was fixed.
+* GNU Privacy Guard was patched to no longer [warn about an "invalid format"](https://github.com/git-for-windows/git/issues/2743) when private and public keys are stored separately.
 
 ## Changes since Git for Windows v2.27.0 (June 1st 2020)