Fix: Branch Param As String

Branches should always be a `string`, otherwise tags like `21.12`
are parsed as floats, which leads to errors such as:
```
  File "regression_testing/repo.py", line 38, in get_branch_name
    return self.branch_wanted.strip("\"")
AttributeError: 'float' object has no attribute 'strip'
```

Author: ax3l

params.py

@@ -100,7 +100,7 @@ def load_params(args):
     # AMReX -- this will always be defined
     rdir = mysuite.check_test_dir(safe_get(cp, "AMReX", "dir"))
 
-    branch = convert_type(safe_get(cp, "AMReX", "branch"))
+    branch = safe_get(cp, "AMReX", "branch")  # note: always as string
     rhash = convert_type(safe_get(cp, "AMReX", "hash"))
 
     mysuite.repos["AMReX"] = repo.Repo(mysuite, rdir, "AMReX",
@@ -127,7 +127,7 @@ def load_params(args):
             k = "source"
 
         rdir = mysuite.check_test_dir(safe_get(cp, s, "dir"))
-        branch = convert_type(safe_get(cp, s, "branch"))
+        branch = safe_get(cp, s, "branch")  # note: always as string
         rhash = convert_type(safe_get(cp, s, "hash"))