Update CI configuration

- Ignore *.md files from the CI pipeline and remove a useless
  strategy block because the job does not use a matrix strategy
- Add Ruby 3.4 to the CI matrix
- Update JRuby for Ubuntu 24.04 compatibility.

.github/workflows/test.yaml

@@ -4,9 +4,13 @@ on:
   push:
     branches:
       - "*"
+    paths-ignore:
+      - '**/*.md'
   pull_request:
     branches:
       - "*"
+    paths-ignore:
+      - '**/*.md'
 jobs:
   lint:
     name: Rubocop
@@ -29,7 +33,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: ["3.3", "3.2", "3.1", "3.0", "2.7", "2.6", "jruby-9.3.6.0"]
+        ruby: ["3.4", "3.3", "3.2", "3.1", "3.0", "2.7", "2.6", "jruby"]
     runs-on: ubuntu-latest
     env:
       LOW_TIMEOUT: "0.01"
@@ -178,8 +182,6 @@ jobs:
   sentinel:
     name: Sentinel
     timeout-minutes: 15
-    strategy:
-      fail-fast: false
     runs-on: ubuntu-latest
     env:
       LOW_TIMEOUT: "0.14"