fix unary operator expected error (#146)

* fix unary operator expected error

The if comparisons can sometimes compare an empty variable, which gives errors like this:
```
/steps/run_tests.sh: line 71: [: =: unary operator expected
```

This PR should fix the script to address that problem. 
See an explanation of why this error happens here:
https://codefather.tech/blog/bash-unary-operator-expected/

* fix missing quote

* Posix shell compliance

Posix shell does not do ==,  it only does one =

* consistent spaces

action/steps/run_tests.sh

@@ -67,8 +67,8 @@ ls -alh $UNITY_PROJECT_PATH
 #
 # Testing in EditMode
 #
-
-if [ $EDIT_MODE = true ]; then
+EDIT_MODE_EXIT_CODE=0
+if [ "$EDIT_MODE" = "true" ]; then
   echo ""
   echo "###########################"
   echo "#   Testing in EditMode   #"
@@ -104,8 +104,8 @@ fi
 #
 # Testing in PlayMode
 #
-
-if [ $PLAY_MODE = true ]; then
+PLAY_MODE_EXIT_CODE=0
+if [ "$PLAY_MODE" = "true" ]; then
   echo ""
   echo "###########################"
   echo "#   Testing in PlayMode   #"
@@ -149,7 +149,7 @@ echo "###########################"
 echo ""
 ls -alh $UNITY_PROJECT_PATH
 
-if [ $EDIT_MODE = true ]; then
+if [ "$EDIT_MODE" = "true" ]; then
   echo ""
   echo "###########################"
   echo "#    Edit Mode Results    #"
@@ -159,7 +159,7 @@ if [ $EDIT_MODE = true ]; then
   cat "$FULL_ARTIFACTS_PATH/editmode-results.xml" | grep test-run | grep Passed
 fi
 
-if [ $PLAY_MODE = true ]; then
+if [ "$PLAY_MODE" = "true" ]; then
   echo ""
   echo "###########################"
   echo "#    Play Mode Results    #"