workflows: don't assume branch existence means the PR is open

.github/workflows/sorbet.yml

@@ -44,7 +44,6 @@ jobs:
             git reset --hard origin/master
           else
             git checkout -B "$BRANCH" origin/master
-            BRANCH_EXISTS="1"
           fi
 
           if brew typecheck --update --fail-if-not-changed; then
@@ -52,7 +51,8 @@ jobs:
             git commit -m "sorbet: Update RBI files." \
                        -m "Autogenerated by the [sorbet](https://github.com/Homebrew/brew/blob/master/.github/workflows/sorbet.yml) workflow."
             echo "::set-output name=committed::true"
-            if [ -n "$BRANCH_EXISTS" ]; then
+            PULL_REQUEST_STATE=$(gh pr view --json=state 2>/dev/null)
+            if [ "$PULL_REQUEST_STATE" != "OPEN" ]; then
               echo "::set-output name=pull_request::true"
             fi
           fi

.github/workflows/spdx.yml

@@ -41,14 +41,14 @@ jobs:
             git reset --hard origin/master
           else
             git checkout -B "$BRANCH" origin/master
-            BRANCH_EXISTS="1"
           fi
 
           if brew update-license-data --fail-if-not-changed; then
             git add "$GITHUB_WORKSPACE/Library/Homebrew/data/spdx"
             git commit -m "spdx: update license data." -m "Autogenerated by [a scheduled GitHub Action](https://github.com/Homebrew/brew/blob/master/.github/workflows/spdx.yml)."
             echo "::set-output name=committed::true"
-            if [ -n "$BRANCH_EXISTS" ]; then
+            PULL_REQUEST_STATE=$(gh pr view --json=state 2>/dev/null)
+            if [ "$PULL_REQUEST_STATE" != "OPEN" ]; then
               echo "::set-output name=pull_request::true"
             fi
           fi

.github/workflows/update-man-completions.yml

@@ -49,7 +49,6 @@ jobs:
             git reset --hard origin/master
           else
             git checkout -B "$BRANCH" origin/master
-            BRANCH_EXISTS="1"
           fi
 
           if [ "${{github.event_name}}" != "push" ]; then
@@ -64,7 +63,8 @@ jobs:
             git commit -m "Update maintainers, manpage and completions." \
                        -m "Autogenerated by the [update-man-completions](https://github.com/Homebrew/brew/blob/HEAD/.github/workflows/update-man-completions.yml) workflow."
             echo "::set-output name=committed::true"
-            if [ -n "$BRANCH_EXISTS" ]; then
+            PULL_REQUEST_STATE=$(gh pr view --json=state 2>/dev/null)
+            if [ "$PULL_REQUEST_STATE" != "OPEN" ]; then
               echo "::set-output name=pull_request::true"
             fi
           fi