Pin versions in GHA jobs (#346)

Author: Mateusz Rzeszutek

.github/workflows/gradle-wrapper-validation.yml

@@ -10,8 +10,8 @@ on:
 
 jobs:
   validation:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v3.0.2
 
       - uses: gradle/[email protected]

.github/workflows/main.yaml

@@ -14,9 +14,10 @@ jobs:
   build:
     runs-on: ubuntu-20.04
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/[email protected]
+
       - name: Set up JDK 11 for running Gradle
-        uses: actions/setup-java@v3
+        uses: actions/setup-java@v3.4.1
         with:
           distribution: adopt
           java-version: 11