apt: skip 'apt-get update' when running from apt already

Do not call 'apt-get update' in post-invoke hook, as APT database is
locked at this time. Since this happens after packages install/update,
it should be already up to date at that point.

Fixes QubesOS/qubes-issues#9673

package-managers/apt-conf-00notify-hook

@@ -1 +1 @@
-DPkg::Post-Invoke {"/usr/lib/qubes/upgrades-status-notify || true";};
+DPkg::Post-Invoke {"/usr/lib/qubes/upgrades-status-notify skip-refresh || true";};

package-managers/upgrades-installed-check

@@ -5,8 +5,16 @@
 ## * 'false' - if there are pending upgrades
 ## * nothing - if apt-get is currently locked
 ##
+## optional argument "skip-refresh" can be used to not refresh metadata (useful
+## when it's already up to date, like after installing updates)
+##
 ## Forwards the exit code of the package manager.
 
+skip_refresh=false
+if [ "$1" = "skip-refresh" ]; then
+    skip_refresh=true
+fi
+
 if [ -e /etc/system-release ]; then
     ## Fedora
     if command -v dnf >/dev/null; then
@@ -23,8 +31,10 @@ elif [ -e /etc/debian_version ]; then
     ## Debian
     set -e
     set -o pipefail
-    # shellcheck disable=SC2034
-    apt_get_update_output="$(apt-get -q update 2>&1 | tee /proc/self/fd/2)"
+    if ! $skip_refresh; then
+        # shellcheck disable=SC2034
+        apt_get_update_output="$(apt-get -q update 2>&1 | tee /proc/self/fd/2)"
+    fi
     apt_get_upgrade_output="$(LANG="C" apt-get -s upgrade 2>&1)"
     exit_code="$?"
     # shellcheck disable=SC2266

package-managers/upgrades-status-notify

@@ -14,7 +14,12 @@ else
     fi
 fi
 
-upgrades_installed="$(/usr/lib/qubes/upgrades-installed-check)"
+script_arg=
+if [ "$1" = "skip-refresh" ]; then
+    script_arg=skip-refresh
+fi
+
+upgrades_installed="$(/usr/lib/qubes/upgrades-installed-check $script_arg)"
 
 if [ "$upgrades_installed" = "true" ]; then
     /usr/lib/qubes/qrexec-client-vm dom0 qubes.NotifyUpdates /bin/sh -c 'echo 0'