ci: fix env var case in workflows (#9877)

**Related Issue:** #9851

## Summary

Fixes the case of environment variables in the workflow files, which I
made uppercase in the GitHub scripts.

.github/workflows/issue-notifications.yaml

@@ -25,7 +25,7 @@ jobs:
         if: github.event.label.name == 'spike complete'
         uses: actions/github-script@v7
         env:
-          managers: ${{secrets.CALCITE_MANAGERS}}
+          MANAGERS: ${{secrets.CALCITE_MANAGERS}}
         with:
           script: |
             const action = require('${{ github.workspace }}/.github/scripts/notifyWhenSpikeComplete.js')
@@ -35,7 +35,7 @@ jobs:
         if: github.event.label.name == 'ready for dev'
         uses: actions/github-script@v7
         env:
-          managers: ${{secrets.CALCITE_MANAGERS}}
+          MANAGERS: ${{secrets.CALCITE_MANAGERS}}
         with:
           script: |
             const action = require('${{ github.workspace }}/.github/scripts/notifyWhenReadyForDev.js')
@@ -45,7 +45,7 @@ jobs:
         if: github.event.label.name == 'new component'
         uses: actions/github-script@v7
         env:
-          designers: ${{secrets.CALCITE_DESIGNERS}}
+          DESIGNERS: ${{secrets.CALCITE_DESIGNERS}}
         with:
           script: |
             const action = require('${{ github.workspace }}/.github/scripts/notifyAboutNewComponent.js')