git: update.sh fix grep warning

pkgs/applications/version-management/git/update.sh

···
 set -eu -o pipefail
 
 oldVersion="$(nix-instantiate --eval -E "with import ./. {}; lib.getVersion git" | tr -d '"')"
-latestTag="$(git ls-remote --tags --sort="v:refname" https://github.com/git/git.git | grep -v '\{\}' | grep -v '\-rc' | tail -1 | sed 's|^.*/v\(.*\)|\1|')"
+latestTag="$(git ls-remote --tags --sort="v:refname" https://github.com/git/git.git | grep -v '{}' | grep -v '\-rc' | tail -1 | sed 's|^.*/v\(.*\)|\1|')"
 targetVersion="${1:-$latestTag}"
 
 if [ ! "${oldVersion}" = "${targetVersion}" ]; then