correct healthcheck su=user parsing error

Thanks @yosifkit (ref:
https://github.com/docker-library/official-images/pull/11864#issuecomment-1045549106)

10.2/healthcheck.sh

@@ -242,7 +242,7 @@ _test_exists() {
 while [ $# -gt 0 ]; do
 	case "$1" in
 		--su=*)
-			u="${1#*-}"
+			u="${1#*=}"
 			shift
 			exec gosu "${u}" "${BASH_SOURCE[0]}" "$@"
 			;;

10.3/healthcheck.sh

@@ -242,7 +242,7 @@ _test_exists() {
 while [ $# -gt 0 ]; do
 	case "$1" in
 		--su=*)
-			u="${1#*-}"
+			u="${1#*=}"
 			shift
 			exec gosu "${u}" "${BASH_SOURCE[0]}" "$@"
 			;;

10.4/healthcheck.sh

@@ -242,7 +242,7 @@ _test_exists() {
 while [ $# -gt 0 ]; do
 	case "$1" in
 		--su=*)
-			u="${1#*-}"
+			u="${1#*=}"
 			shift
 			exec gosu "${u}" "${BASH_SOURCE[0]}" "$@"
 			;;

10.5/healthcheck.sh

@@ -242,7 +242,7 @@ _test_exists() {
 while [ $# -gt 0 ]; do
 	case "$1" in
 		--su=*)
-			u="${1#*-}"
+			u="${1#*=}"
 			shift
 			exec gosu "${u}" "${BASH_SOURCE[0]}" "$@"
 			;;

10.6/healthcheck.sh

@@ -242,7 +242,7 @@ _test_exists() {
 while [ $# -gt 0 ]; do
 	case "$1" in
 		--su=*)
-			u="${1#*-}"
+			u="${1#*=}"
 			shift
 			exec gosu "${u}" "${BASH_SOURCE[0]}" "$@"
 			;;

10.7/healthcheck.sh

@@ -242,7 +242,7 @@ _test_exists() {
 while [ $# -gt 0 ]; do
 	case "$1" in
 		--su=*)
-			u="${1#*-}"
+			u="${1#*=}"
 			shift
 			exec gosu "${u}" "${BASH_SOURCE[0]}" "$@"
 			;;

10.8/healthcheck.sh

@@ -242,7 +242,7 @@ _test_exists() {
 while [ $# -gt 0 ]; do
 	case "$1" in
 		--su=*)
-			u="${1#*-}"
+			u="${1#*=}"
 			shift
 			exec gosu "${u}" "${BASH_SOURCE[0]}" "$@"
 			;;

healthcheck.sh

@@ -242,7 +242,7 @@ _test_exists() {
 while [ $# -gt 0 ]; do
 	case "$1" in
 		--su=*)
-			u="${1#*-}"
+			u="${1#*=}"
 			shift
 			exec gosu "${u}" "${BASH_SOURCE[0]}" "$@"
 			;;