test action with PR trigger and older Rust version

Author: szokeasaurusrex

.github/workflows/rust-toolchain-update.yml

@@ -4,6 +4,7 @@ on:
   schedule:
     # Run weekly on Mondays at 00:00 UTC
     - cron: '0 0 * * 1'
+  pull_request:
 
 jobs:
   check-and-update:
@@ -106,7 +107,7 @@ jobs:
               repo: context.repo.repo,
               title: commitTitle,
               head: branchName,
-              base: '${{ github.ref_name }}',
+              base: '${{ github.head_ref }}',
               body: `Update Rust toolchain to ${newVersion} (${fullVersion}).
 
                     **Changes:**

rust-toolchain.toml

@@ -1,4 +1,4 @@
 [toolchain]
 # We pin the minor version to prevent new Clippy lints from breaking CI.
 # But, we still want to pick up new patch versions.
-channel = "1.89"
+channel = "1.88"