only one PR for GitHub actions updates (#179)

Author: ranocha

.github/dependabot.yml

@@ -5,3 +5,11 @@ updates:
     directory: "/" # Location of package manifests
     schedule:
       interval: "monthly"
+    groups:
+      # Group all GitHub Actions PRs into a single PR:
+      all-github-actions:
+        patterns:
+          - "*"
+    ignore:
+      - dependency-name: "julia-actions/julia-downgrade-compat"
+        versions: [ ">=2.0.0" ]

docs/make.jl

@@ -101,4 +101,7 @@ makedocs(modules = [PositiveIntegrators, Base.get_extension(PositiveIntegrators,
 
 deploydocs(repo = "github.com/NumericalMathematics/PositiveIntegrators.jl",
            devbranch = "main",
-           push_preview = true)
+           # Only push previews if all the relevant environment variables are non-empty.
+           push_preview = all(!isempty,
+                              (get(ENV, "GITHUB_TOKEN", ""),
+                               get(ENV, "DOCUMENTER_KEY", ""))))