CI image builder: fix profile loading for gentoo

We need to load various environment variables from /etc/profile. We
cannot unconditionally load it, because opensuse sources env_vars and
their /etc/profile has a fatal bug in it that causes it to return
nonzero and abort under `set -e` (which is *amazing* as a thing to have
in /etc/profile specifically -- just saying).

Alas, even /etc/profile.env is not enough since Java support depends on
profile.d logic. Re-conditionalize this check to only be added to
env_vars.sh for the image named "gentoo".

.github/workflows/images.yml

@@ -7,7 +7,6 @@ concurrency:
 on:
   push:
     branches:
-      - master
     paths:
       - 'ci/ciimage/**'
       - '.github/workflows/images.yml'

ci/ciimage/build.py

@@ -78,10 +78,11 @@ class Builder(BuilderBase):
             if [ -f "$HOME/.cargo/env" ]; then
                 source "$HOME/.cargo/env"
             fi
+        '''
 
-            if [ -f /etc/profile.env ]; then
-                source /etc/profile.env
-            fi
+        if self.data_dir.name == 'gentoo':
+            out_data += '''
+                source /etc/profile
             '''
 
         out_file.write_text(out_data, encoding='utf-8')