EBAS reader: open db in read only mode only

[jgriesfeller]

Change Summary

the title says it all

Related issue number

fix #1232

Checklist

• Start with a draft-PR
• The PR title is a good summary of the changes
• PR is set to AeroTools and a tentative milestone
• Documentation reflects the changes where applicable
• Tests for the changes exist where applicable
• Tests pass locally
• Tests pass on CI
• At least 1 reviewer is selected
• Make PR ready to review

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.30%. Comparing base (a95b5c2) to head (f453e71).
Report is 457 commits behind head on main-dev.

Additional details and impacted files

@@            Coverage Diff            @@
##           main-dev    #1233   +/-   ##
=========================================
  Coverage     79.30%   79.30%           
=========================================
  Files           131      131           
  Lines         20238    20245    +7     
=========================================
+ Hits          16049    16056    +7     
  Misses         4189     4189           

Flag	Coverage Δ
unittests	79.30% <100.00%> (+<0.01%)	⬆️

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[lewisblake]

thanks