Gentoo emerge: add --autounmask-write (the missing piece for ~amd64)

Discovered via man: --autounmask=y alone only DISPLAYS the needed
keyword changes and aborts. The actual write to /etc/portage/...
files requires --autounmask-write=y (or --autounmask-continue=y
which also auto-continues after writing). Without --autounmask-write,
every lazygit (and any other ~amd64-only GURU package) install
fails with:

  The following keyword changes are necessary to proceed:
  =dev-vcs/lazygit-0.62.2 ~amd64
  Use --autounmask-write to write changes to config files

Added to all three emerge invocations:
- run_once_20-install-user-packages-gentoo.sh.tmpl: main loop
- run_once_20-install-user-packages-gentoo.sh.tmpl: GURU loop
- run_once_40-install-sway-gentoo.sh.tmpl

run_once_20-install-user-packages-gentoo.sh.tmpl

@@ -139,11 +139,12 @@ if (( ${#MISSING_PKGS[@]} > 0 )); then
     # --quiet-build: only show errors during compile
     # --keep-going: don't abort if one package fails
     # --with-bdeps=y: include build deps so we don't accidentally skip them
-    # --autounmask=y: auto-write ~amd64 keyword unmask files (lazygit
-    #   is ~amd64 only)
+    # --autounmask=y --autounmask-write=y: auto-write ~amd64 keyword
+    #   unmask files (lazygit is ~amd64 only). Without --autounmask-write,
+    #   emerge only DISPLAYS the needed changes and aborts.
     # --autounmask-license=y: auto-accept license unmask
     sudo emerge --ask=n --nospinner --quiet-build --keep-going \
-        --with-bdeps=y --autounmask=y --autounmask-license=y \
+        --with-bdeps=y --autounmask=y --autounmask-write=y --autounmask-license=y \
         "${MISSING_PKGS[@]}"
 else
     log "all user packages already installed; skipping emerge"
@@ -183,7 +184,7 @@ done
 if (( ${#GURU_MISSING[@]} > 0 )); then
     log "emerge GURU packages (missing: ${GURU_MISSING[*]})"
     sudo emerge --ask=n --nospinner --quiet-build --keep-going \
-        --with-bdeps=y --autounmask=y --autounmask-license=y \
+        --with-bdeps=y --autounmask=y --autounmask-write=y --autounmask-license=y \
         "${GURU_MISSING[@]}"
 fi
 

run_once_40-install-sway-gentoo.sh.tmpl

@@ -71,7 +71,7 @@ if (( ${#MISSING_PKGS[@]} > 0 )); then
     log "missing: ${MISSING_PKGS[*]}"
     log "emerge sway stack (gentoo compiles from source; this may take a while)"
     sudo emerge --ask=n --nospinner --quiet-build --keep-going \
-        --with-bdeps=y --autounmask=y --autounmask-license=y \
+        --with-bdeps=y --autounmask=y --autounmask-write=y --autounmask-license=y \
         "${MISSING_PKGS[@]}"
 else
     log "all sway packages already installed; skipping emerge"