prevent spreadsheet export and invoice from breaking

[kevinpapst]

Description

apply fixes to prevent export and invoice from breaking if a description starts with an = equal sign

Fixes #2014

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I verified that my code applies to the guidelines (composer code-check)
• I updated the documentation (see here)
• I agree that this code is used in Kimai and will be published under the MIT license

[codecov]

Codecov Report

Merging #2054 into master will decrease coverage by 0.05%.
The diff coverage is 75.00%.

@@             Coverage Diff              @@
##             master    #2054      +/-   ##
============================================
- Coverage     93.33%   93.27%   -0.06%     
- Complexity     5787     5788       +1     
============================================
  Files           530      530              
  Lines         17536    17538       +2     
============================================
- Hits          16367    16359       -8     
- Misses         1169     1179      +10     

Impacted Files	Coverage Δ	Complexity Δ
...c/Invoice/Renderer/AbstractSpreadsheetRenderer.php	94.20% <66.66%> (-1.32%)	26.00 <0.00> (+1.00)	⬇️
src/Export/Base/AbstractSpreadsheetRenderer.php	91.28% <100.00%> (ø)	115.00 <0.00> (ø)
src/Invoice/Renderer/AdvancedValueBinder.php	46.66% <0.00%> (-53.34%)	6.00% <0.00%> (ø%)
src/Repository/TimesheetRepository.php	89.35% <0.00%> (-0.20%)	133.00% <0.00%> (ø%)