CompatHelper: bump compat for Bijectors to 0.15, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the Bijectors package from 0.13.18, 0.14 to 0.13.18, 0.14, 0.15.
This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry.
It is your responsibility to make sure that your package tests pass before you merge this pull request.

[coveralls]

Pull Request Test Coverage Report for Build 12083954600

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 26 unchanged lines in 5 files lost coverage.
• Overall coverage decreased (-0.02%) to 86.367%

---

Files with Coverage Reduction	New Missed Lines	%
src/model.jl	1	91.58%
src/test_utils.jl	1	50.0%
src/varinfo.jl	6	86.3%
src/simple_varinfo.jl	6	86.6%
src/threadsafe.jl	12	59.48%

Totals
Change from base Build 12083280383:	-0.02%
Covered Lines:	3611
Relevant Lines:	4181

---

💛 - Coveralls

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.38%. Comparing base (1110d30) to head (3d10037).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #731   +/-   ##
=======================================
  Coverage   86.38%   86.38%           
=======================================
  Files          35       35           
  Lines        4180     4180           
=======================================
  Hits         3611     3611           
  Misses        569      569           

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