Bump slackapi/slack-github-action from 1.25.0 to 1.26.0 (#5394)

Bumps [slackapi/slack-github-action](https://github.com/slackapi/slack-github-action) from 1.25.0 to 1.26.0.
- [Release notes](https://github.com/slackapi/slack-github-action/releases)
- [Commits](slackapi/slack-github-action@v1.25.0...v1.26.0)

---
updated-dependencies:
- dependency-name: slackapi/slack-github-action
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/create-docs-issues.yml

@@ -25,7 +25,7 @@ jobs:
             await script({github, context});
 
       - name: Slack Failure Message
-        uses: slackapi/slack-github-action@v1.25.0
+        uses: slackapi/slack-github-action@v1.26.0
         id: slack-failure-message
         if: failure() && github.ref == 'refs/heads/main' && github.repository_owner == 'deephaven'
         env:

.github/workflows/nightly-check-ci.yml

@@ -101,7 +101,7 @@ jobs:
           report_paths: '**/build/test-results/*/TEST-*.xml'
 
       - name: Slack Nightly Failure
-        uses: slackapi/slack-github-action@v1.25.0
+        uses: slackapi/slack-github-action@v1.26.0
         id: slack-nightly-failure
         if: ${{ failure() && github.repository_owner == 'deephaven' }}
         with:

.github/workflows/nightly-image-check.yml

@@ -36,7 +36,7 @@ jobs:
           gradle-version: wrapper
 
       - name: Notify Slack
-        uses: slackapi/slack-github-action@v1.25.0
+        uses: slackapi/slack-github-action@v1.26.0
         id: notify-slack
         if: ${{ failure() }}
         env: