ci: update actions to latest versions
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 42bf7c5..afc6ca2 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -52,17 +52,17 @@
 
     steps:
     - name: Install Go
-      uses: actions/setup-go@v2
+      uses: actions/setup-go@v5
       with:
         go-version: ${{ matrix.go-version }}
 
     - name: Checkout code
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
       with:
           path: ${{ env.GOPATH }}/src/gonum.org/v1/gonum
 
     - name: Cache-Go
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       with:
         # In order:
         # * Module download cache 
diff --git a/.github/workflows/codecov.yml b/.github/workflows/codecov.yml
index f842844..4b7f467 100644
--- a/.github/workflows/codecov.yml
+++ b/.github/workflows/codecov.yml
@@ -32,17 +32,17 @@
 
     steps:
     - name: Install Go
-      uses: actions/setup-go@v2
+      uses: actions/setup-go@v5
       with:
         go-version: ${{ matrix.go-version }}
 
     - name: Checkout code
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
       with:
         path: ${{ env.GOPATH }}/src/gonum.org/v1/gonum
 
     - name: Cache-Go
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       with:
         # In order:
         # * Module download cache
diff --git a/.github/workflows/staticcheck.yml b/.github/workflows/staticcheck.yml
index cce9575..c5486c0 100644
--- a/.github/workflows/staticcheck.yml
+++ b/.github/workflows/staticcheck.yml
@@ -10,7 +10,7 @@
     env:
         GO111MODULE: on
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
       with:
         fetch-depth: 1
     - uses: dominikh/staticcheck-action@v1