Act env (#417)

* Test more if env variants

* The correct negation syntax is !=

* Make the Interpolate function support negated booleans from envs

* Move assert := a.New(t) into t.Run

This uncovered that some of the test premisses was wrong and the
Eval Bool function also had flaws

* Remove a stray logrus import

* Add an ACT env set to true

This can be used to skip certain steps that you don't want to run locally
when testing. E.g. steps that sends messages to Slack channels on successful
builds etc.

* Add a description about env.ACT to the readme

* A new attempt at Interpolation and EvalBool

* One small merge fix

* Remove some fmt.Printfs

* Fix some merge conflicts

.github/workflows/test-if.yml

@@ -6,6 +6,7 @@ env:
   SOMETHING_TRUE: true
   SOMETHING_FALSE: false
   SOME_TEXT: text
+  ACT: true
 
 
 jobs:
@@ -389,3 +390,17 @@ jobs:
      - name: "Double checking expr: true && €{{ env.SOMETHING_FALSE == 'true' }}"
        if: steps.step57.conclusion == 'skipped'
        run: echo "true && ${{ env.SOMETHING_FALSE == 'true' }} should have been true, but wasn't"
+
+     - name: "✅ I should run, expr: €{{ env.ACT }}"
+       id: step60
+       if: ${{ env.ACT }}
+       run: echo OK
+
+     - name: "Double checking expr: €{{ env.ACT }}"
+       if: steps.step60.conclusion == 'skipped'
+       run: echo "${{ env.ACT }} should have been true, but wasn't"
+
+     - name: "❌ I should not run, expr: €{{ !env.ACT }}"
+       id: step61
+       if: ${{ !env.ACT }}
+       run: echo "${{ !env.ACT }} should be false, but was evaluated to true;" exit 1;