Handle general problems with pull request

When possible, if problems are detected in a pull request, the bot will attempt to guide the PR author through the
process of making a valid submission, which should be handled in a completely automated fashion on our end.

It has become clear that we need to prevent the removal of the final newline from `repositories.txt`. The existing system
did not accomodate this requirement. Submissions are validated on a per-library basis, and the bot comments based on
identifying which library the problem applies to. But this newline removal is not necessarily related to any specific
item added to the list. So handling for general problems with a submission PR is needed, which is added here.

Because the PR author is more likely to require assistance with resolving this sort of problem, PR review from a
maintainer is requested.

.github/workflows/manage-prs.yml

@@ -93,6 +93,7 @@ jobs:
 
     outputs:
       type: ${{ steps.parse-request.outputs.type }}
+      error: ${{ steps.parse-request.outputs.error }}
       arduinoLintLibraryManagerSetting: ${{ steps.parse-request.outputs.arduinoLintLibraryManagerSetting }}
       submissions: ${{ steps.parse-request.outputs.submissions }}
       index-entry: ${{ steps.parse-request.outputs.index-entry }}
@@ -133,6 +134,7 @@ jobs:
           # Due to limitations of the GitHub Actions workflow system, dedicated outputs must be created for use in
           # certain workflow fields.
           echo "::set-output name=type::$(echo "$REQUEST" | jq -r -c '.type')"
+          echo "::set-output name=error::$(echo "$REQUEST" | jq -r -c '.error')"
           echo "::set-output name=arduinoLintLibraryManagerSetting::$(echo "$REQUEST" | jq -r -c '.arduinoLintLibraryManagerSetting')"
           echo "::set-output name=submissions::$(echo "$REQUEST" | jq -c '.submissions')"
           echo "::set-output name=index-entry::$(echo "$REQUEST" | jq -r -c '.indexEntry')"
@@ -156,6 +158,34 @@ jobs:
           labels: |
             - ${{ needs.parse.outputs.type }}
 
+  parse-fail:
+    needs:
+      - parse
+    if: needs.parse.outputs.error != ''
+
+    runs-on: ubuntu-latest
+    steps:
+      - name: Comment on error detected while parsing PR
+        uses: octokit/request-action@v2.x
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          route: POST /repos/{owner}/{repo}/issues/{issue_number}/comments
+          owner: ${{ github.repository_owner }}
+          repo: ${{ github.event.repository.name }}
+          issue_number: ${{ github.event.pull_request.number }}${{ github.event.issue.number }}
+          body: |
+            |
+            Hi @${{ github.actor }}
+            A problem was found with your pull request:
+
+            ${{ env.ERROR_MESSAGE_PREFIX }}${{ needs.parse.outputs.error }}
+
+            Please resolve this error. The checks will automatically run again once that is done.
+
+            More information:
+            https://github.com/${{ github.repository }}/blob/main/README.md#if-the-problem-is-with-the-pull-request
+
   check-submissions:
     name: Check ${{ matrix.submission.submissionURL }}
     needs:
@@ -473,7 +503,10 @@ jobs:
   not-submission:
     needs:
       - parse
-    if: needs.parse.outputs.type != 'submission' # These request types can't be automatically approved.
+    # These request types can't be automatically approved.
+    if: >
+      needs.parse.outputs.type != 'submission' &&
+      needs.parse.outputs.type != 'invalid'
     runs-on: ubuntu-latest
     steps:
       - name: Comment on required review
@@ -497,6 +530,7 @@ jobs:
   unexpected-fail:
     needs:
       # Run after all other jobs
+      - parse-fail
       - merge-fail
       - check-submissions-fail
       - label
@@ -548,12 +582,14 @@ jobs:
 
   request-review:
     needs:
+      - parse-fail
       - merge-fail
       - not-submission
       - unexpected-fail
     if: >
       always() &&
       (
+        needs.parse-fail.result != 'skipped' ||
         needs.merge-fail.result != 'skipped' ||
         needs.not-submission.result != 'skipped' ||
         needs.unexpected-fail.result != 'skipped'