chore: Add ability to deal with temporary files generated by tests

The "install_nextflow" tests generate a new install of Nextflow every time
 they are run based on the "RUNNER_TEMP" environment variable. Deal with
this by adding our RUNNER_TEMP variable to the ava config and making sure
none of these installs get committed.

.gitignore

@@ -132,3 +132,7 @@ dist
 # Ignore built ts files
 __tests__/runner/*
 lib/**/*
+
+# Testing garbage
+.tmp
+nxf-v*

package.json

@@ -28,6 +28,9 @@
     "extensions": [
       "ts"
     ],
+    "environmentVariables": {
+      "RUNNER_TEMP": "./.tmp"
+    },
     "rewritePaths": {
       "src/": "lib/"
     },