github: adjust stale workflow

This commit adjusts the stale workflow so that it only closes stale test
failures and sentry issues. Previously, it would close all issues with
no activity in the last 18 months (modulo some exempted labels), but I
don't think it's helpful to close issues filed by humans in this way - we
might still want to track a particular bug or a feature in order to gauge
the urgency. Closing stale (no activity in 12 months) test failures (as
defined by having `C-test-failure` label) and sentry issues seems like
a good idea though.

This commit also removes a few fields that are related to stale PRs since
we don't do anything for them (because we use very large "inactivity"
window).

Release note: None

.github/workflows/stale.yml

@@ -1,4 +1,4 @@
-name: Mark stale issues and pull requests
+name: Close stale test failures and sentry issues
 
 on:
   schedule:
@@ -18,17 +18,14 @@ jobs:
         repo-token: ${{ secrets.GITHUB_TOKEN }}
         stale-issue-message: |
            We have marked this issue as stale because it has been inactive for
-           18 months. If this issue is still relevant, removing the stale label
+           12 months. If this issue is still relevant, removing the stale label
            or adding a comment will keep it active. Otherwise, we'll close it in
-           10 days to keep the issue queue tidy. Thank you for your contribution
-           to CockroachDB!
-        stale-pr-message: 'Stale pull request message'
+           10 days to keep the issue queue tidy.
         stale-issue-label: 'no-issue-activity'
-        stale-pr-label: 'no-pr-activity'
         close-issue-label: 'X-stale'
-        close-pr-label: 'X-stale'
         # Disable this for PR's, by setting a very high bar
         days-before-pr-stale: 99999
-        days-before-issue-stale: 540
+        days-before-issue-stale: 366
         days-before-close: 10
+        any-of-issue-labels: 'C-test-failure,O-sentry'
         exempt-issue-labels: 'release-blocker,X-anchored-telemetry,X-nostale'