Pin SHA of third-party GitHub Actions (#248)

The full-version Git tags used by Actions are mutable (as seen in recent
events in the wider GitHub Actions community), so pinning third-party
Actions to a SHA is recommended:
https://docs.github.com/en/actions/security-for-github-actions/security-guides/security-hardening-for-github-actions#using-third-party-actions

The version tag has been added after the pin as a comment (as a
readability aid) in a format that Dependabot will keep up to date:
dependabot/dependabot-core#4691

I've also enabled Dependabot grouping for GitHub Actions updates
to reduce PR noise.

GUS-W-18051077.

Author: edmorley

.github/dependabot.yml

@@ -34,3 +34,8 @@ updates:
     labels:
       - "dependencies"
       - "skip changelog"
+    groups:
+      github-actions:
+        update-types:
+          - "minor"
+          - "patch"

.github/workflows/ci.yml

@@ -70,7 +70,7 @@ jobs:
       - name: Update Rust toolchain
         run: rustup update
       - name: Rust Cache
-        uses: Swatinem/[email protected]
+        uses: Swatinem/rust-cache@f0deed1e0edfc6a9be95417288c0e1099b1eeec3 # v2.7.7
         with:
           workspaces: "./integration-test"
       - uses: actions/download-artifact@v4
@@ -87,7 +87,7 @@ jobs:
       - name: Update Rust toolchain
         run: rustup update
       - name: Rust Cache
-        uses: Swatinem/[email protected]
+        uses: Swatinem/rust-cache@f0deed1e0edfc6a9be95417288c0e1099b1eeec3 # v2.7.7
         with:
           workspaces: "./integration-test"
       - name: Clippy

.github/workflows/prepare-release.yml

@@ -58,7 +58,7 @@ jobs:
 
       - name: Create pull request
         id: pr
-        uses: peter-evans/[email protected].6
+        uses: peter-evans/create-pull-request@271a8d0340265f705b14b6d32b9829c1cb33d45e # v7.0.8
         with:
           token: ${{ steps.generate-token.outputs.token }}
           title: Prepare release v${{ steps.new-version.outputs.version }}

.github/workflows/release.yml

@@ -73,7 +73,7 @@ jobs:
           MAVEN_GPG_PASSPHRASE: ${{ secrets.MAVEN_GPG_PASSPHRASE }}
 
       - name: Create GitHub Release
-        uses: softprops/[email protected]
+        uses: softprops/action-gh-release@c95fe1489396fe8a9eb87c0abf8aa5b2ef267fda # v2.2.1
         with:
           token: ${{ steps.generate-token.outputs.token }}
           tag_name: v${{ steps.new-version.outputs.version }}
@@ -88,7 +88,7 @@ jobs:
 
       - name: Create pull request
         id: pr
-        uses: peter-evans/[email protected].6
+        uses: peter-evans/create-pull-request@271a8d0340265f705b14b6d32b9829c1cb33d45e # v7.0.8
         with:
           token: ${{ steps.generate-token.outputs.token }}
           title: Prepare next development iteration ${{ steps.next-version.outputs.version }}