Add comments where concurrency is not required so that it is considered when making changes.

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

@@ -5,6 +5,7 @@ jobs:
   validation:
     name: "Validation"
     runs-on: ubuntu-latest
+    # No concurrency required, this is a prerequisite to other actions and should run every time.
     steps:
       - uses: actions/checkout@v2
       - uses: gradle/wrapper-validation-action@v1

.github/workflows/sanity_test.yml

@@ -19,6 +19,7 @@ jobs:
       fail-fast: false
       matrix:
         api-level: [ 28 ]
+    # No concurrency required, runs every time on a schedule.
     steps:
       - uses: actions/checkout@v2
         with:

.github/workflows/sync-from-external-sources.yml

@@ -9,6 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     # Skip in forks
     if: github.repository == 'vector-im/element-android'
+    # No concurrency required, runs every time on a schedule.
     steps:
       - uses: actions/checkout@v2
       - name: Set up Python 3.8
@@ -43,6 +44,7 @@ jobs:
     runs-on: ubuntu-latest
     # Skip in forks
     if: github.repository == 'vector-im/element-android'
+    # No concurrency required, runs every time on a schedule.
     steps:
       - uses: actions/checkout@v2
       - name: Set up Python 3.8
@@ -76,6 +78,7 @@ jobs:
     runs-on: ubuntu-latest
     # Skip in forks
     if: github.repository == 'vector-im/element-android'
+    # No concurrency required, runs every time on a schedule.
     steps:
       - uses: actions/checkout@v2
       - name: Run analytics import script