DS-970: Add Magic Nix Cache and other workflow changes

An assortment of GitHub Workflow changes, potentially including:

- Enable DeterminateSystems/magic-nix-cache-action@main
- Reference all DeterminateSystems actions via @main
- Make update.yaml consistent across repos
- Remove unnecessary github-token: from nix-installer-action
- Update actions/checkout@v2 to actions/checkout@v3

.github/workflows/build.yaml

@@ -10,8 +10,9 @@ jobs:
     steps:
       - uses: actions/checkout@v3
 
-      - uses: DeterminateSystems/nix-installer-action@v4
-      - uses: DeterminateSystems/magic-nix-cache-action@v2
+      - uses: DeterminateSystems/nix-installer-action@main
+
+      - uses: DeterminateSystems/magic-nix-cache-action@main
 
       - name: Build package
         run: "nix build .# -L"
@@ -29,8 +30,9 @@ jobs:
     steps:
       - uses: actions/checkout@v3
 
-      - uses: DeterminateSystems/nix-installer-action@v4
-      - uses: DeterminateSystems/magic-nix-cache-action@v2
+      - uses: DeterminateSystems/nix-installer-action@main
+
+      - uses: DeterminateSystems/magic-nix-cache-action@main
 
       - name: Build package
         run: "nix build .# -L"

.github/workflows/ci.yml

@@ -11,13 +11,13 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v3
+      - name: Install Nix
+        uses: DeterminateSystems/nix-installer-action@main
+      - uses: DeterminateSystems/magic-nix-cache-action@main
       - name: Check flake.lock
-        uses: DeterminateSystems/flake-checker-action@v4
+        uses: DeterminateSystems/flake-checker-action@main
         with:
           fail-mode: true
-      - name: Install Nix
-        uses: DeterminateSystems/nix-installer-action@v4
-      - uses: DeterminateSystems/magic-nix-cache-action@v2
       - name: Check Nix formatting
         run: nix develop -c check-nixpkgs-fmt
       - name: Check Rust formatting
@@ -31,8 +31,8 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - name: Install Nix
-        uses: DeterminateSystems/nix-installer-action@v4
-      - uses: DeterminateSystems/magic-nix-cache-action@v2
+        uses: DeterminateSystems/nix-installer-action@main
+      - uses: DeterminateSystems/magic-nix-cache-action@main
       - name: cargo test
         run: nix develop -c cargo test
 
@@ -42,8 +42,8 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - name: Install Nix
-        uses: DeterminateSystems/nix-installer-action@v4
-      - uses: DeterminateSystems/magic-nix-cache-action@v2
+        uses: DeterminateSystems/nix-installer-action@main
+      - uses: DeterminateSystems/magic-nix-cache-action@main
       - name: Check flake.lock
         run: |
           nix develop -c cargo run -- ./tests/flake.dirty.0.lock
@@ -54,8 +54,8 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - name: Install Nix
-        uses: DeterminateSystems/nix-installer-action@v4
-      - uses: DeterminateSystems/magic-nix-cache-action@v2
+        uses: DeterminateSystems/nix-installer-action@main
+      - uses: DeterminateSystems/magic-nix-cache-action@main
       - name: Check flake.lock
         run: |
           nix develop -c cargo run
@@ -67,8 +67,8 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - name: Install Nix
-        uses: DeterminateSystems/nix-installer-action@v4
-      - uses: DeterminateSystems/magic-nix-cache-action@v2
+        uses: DeterminateSystems/nix-installer-action@main
+      - uses: DeterminateSystems/magic-nix-cache-action@main
       - name: Check flake.lock
         run: |
           nix develop -c cargo run -- --fail-mode ./tests/flake.dirty.0.lock

.github/workflows/udpate-flake-lock.yml

@@ -10,8 +10,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
-      - uses: DeterminateSystems/nix-installer-action@v4
-      - uses: DeterminateSystems/update-flake-lock@v19
+      - uses: DeterminateSystems/nix-installer-action@main
+      - uses: DeterminateSystems/magic-nix-cache-action@main
+      - uses: DeterminateSystems/update-flake-lock@main
         with:
           pr-title: "Update flake.lock"
           pr-labels: |