Fix parsing directories

[JCGoran]

• throw a runtime error if we pass a directory to parse_file (fixes Trying to driver.parse_file('.') exits program #1113)
• add test to make sure it works

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.60%. Comparing base (347f786) to head (c71ecbf).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1203      +/-   ##
==========================================
+ Coverage   86.58%   86.60%   +0.01%     
==========================================
  Files         175      175              
  Lines       13006    13009       +3     
==========================================
+ Hits        11261    11266       +5     
+ Misses       1745     1743       -2     

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[bbpbuildbot]

Logfiles from GitLab pipeline #198874 (:white_check_mark:) have been uploaded here!

Status and direct links:

• ✅ spack_setup
• ✅ build:intel
• ✅ build:nvhpc
• ✅ test:intel
• ✅ test:nvhpc