chore: multiline env var; explicitly check diff against HEAD~1 (#167)

Signed-off-by: Nick Boldt <nboldt@redhat.com>

.github/workflows/next-container-build.yaml

@@ -41,14 +41,18 @@ jobs:
       - name: check-changes
         # check changes in this commit for regex include and exclude matches; pipe to an env var
         run: |
-          CHANGES="$(git diff --name-only | \
+          CHANGES="$(git diff --name-only HEAD~1 | \
           grep -E "docker/|\.dockerignore|workflows/.+-container-build.yaml|Makefile|bundle/|config/|go.mod|go.sum|.+\.go" | \
           grep -v -E ".+_test.go|/.rhdh/")";
           echo "Changed files for this commit:"
           echo "=============================="
           echo "$CHANGES"
           echo "=============================="
-          echo "CHANGES=$CHANGES" >> $GITHUB_ENV
+          {
+            echo 'CHANGES<<EOF'
+            echo $CHANGES
+            echo EOF
+          } >> "$GITHUB_ENV"
 
   next-build:
     name: Next build

.github/workflows/pr-container-build.yaml

@@ -62,14 +62,18 @@ jobs:
       - name: check-changes
         # check changes in this commit for regex include and exclude matches; pipe to an env var
         run: |
-          CHANGES="$(git diff --name-only | \
+          CHANGES="$(git diff --name-only HEAD~1 | \
           grep -E "docker/|\.dockerignore|workflows/.+-container-build.yaml|Makefile|bundle/|config/|go.mod|go.sum|.+\.go" | \
           grep -v -E ".+_test.go|/.rhdh/")";
           echo "Changed files for this commit:"
           echo "=============================="
           echo "$CHANGES"
           echo "=============================="
-          echo "CHANGES=$CHANGES" >> $GITHUB_ENV
+          {
+            echo 'CHANGES<<EOF'
+            echo $CHANGES
+            echo EOF
+          } >> "$GITHUB_ENV"
 
   pr-build:
     name: PR Publish