Add input for number of Julia threads

Author: lkdvos

.github/workflows/Tests.yml

@@ -32,6 +32,11 @@ on:
         default: "ubuntu-latest"
         required: false
         type: string
+      nthreads:
+        description: "The number of Julia threads"
+        default: 1
+        required: false
+        type: number
       cache:
         description: "Use the julia-actions/cache action for caching"
         default: true
@@ -108,6 +113,7 @@ jobs:
           coverage: "${{ inputs.coverage }}"
         env:
           GROUP: "${{ inputs.group }}"
+          JULIA_NUM_THREADS: "${{ inputs.nthreads }}"
 
       - uses: julia-actions/julia-processcoverage@v1
         if: "${{ inputs.coverage }}"