Rename the pin check to "Action pin check"

.github/workflows/premerge.yaml

@@ -19,7 +19,7 @@ jobs:
     # request that makes it.  `actions/` holds the composite actions, whose `uses:` steps need
     # the same pins as any workflow's.
     runs-on: [ubuntu-latest]
-    name: Action pins are immutable
+    name: Action pin check
     timeout-minutes: 5
     steps:
       - name: Check out source repository

README.md

@@ -26,7 +26,7 @@ jobs:
 
   action-pins:
     runs-on: [ubuntu-latest]
-    name: Action pins are immutable
+    name: Action pin check
     timeout-minutes: 5
     steps:
       - uses: actions/checkout@<sha> # vX.Y.Z

actions/action-pins/action.yml

@@ -1,4 +1,4 @@
-name: 'Action pins are immutable'
+name: 'Action pin check'
 description: 'Fail when any `uses:` in the checked-out repository names something other than a full 40-hex commit SHA, or a version tag of L337-org/github-workflows.'
 
 # A tag or branch ref can be repointed by the action's owner at any time, so `@v7` means CI runs