fix(ci): escape brackets in case patterns for bot logins

In POSIX shell case patterns, [bot] is a glob character class that
matches a single character (b/o/t), not the literal string '[bot]'.
This meant release-please[bot], dependabot[bot], and the other bot
exemptions never matched and those PRs would have been failed by
validate-pr-base. Escape the brackets so the patterns match the
actual GitHub App login strings.

Caught by Greptile review.

Author: declan-scale

.github/workflows/lint-pr.yaml

@@ -58,7 +58,7 @@ jobs:
         run: |
           # Exempt automated PRs (Stainless codegen, release-please, dependabot, etc.)
           case "$PR_AUTHOR" in
-            stainless-app|stainless-app[bot]|release-please[bot]|github-actions[bot]|dependabot[bot])
+            stainless-app|stainless-app\[bot\]|release-please\[bot\]|github-actions\[bot\]|dependabot\[bot\])
               echo "PR is from automation ($PR_AUTHOR); allowing PR targeting main."
               exit 0
               ;;