ci: fix "Free Additional disk space" step

Hardcode so tbat it greps built_termux-main_packages.txt instead of
built_packages.txt

.github/workflows/packages.yml

@@ -150,7 +150,7 @@ jobs:
 
     - name: Free additional disk space (if necessary)
       run: |
-        if grep -qP '^rust$' ./built_packages.txt ; then
+        if grep -qP '^rust$' ./built_termux-main_packages.txt ; then
           echo "Free additional disk space on host"
           sudo apt purge -yq $(dpkg -l | grep '^ii' | awk '{ print $2 }' | grep -P '(cabal-|dotnet-|ghc-|libmono|php)') \
             liblldb-6.0 libllvm6.0:amd64 mono-runtime-common monodoc-manual powershell ruby