Temporarily fix Hecke version (oscar-system#4782)

There is an error in the doc build in Oscar with the Hecke release from yesterday.

Author: thofma

Project.toml

@@ -37,7 +37,7 @@ Compat = "4.13.0"
 Distributed = "1.6"
 GAP = "0.13.1"
 GAP_lib_jll = "~400.1400.4" # remove again once GAP.jl requires this version
-Hecke = "0.35.10"
+Hecke = "= 0.35.15"
 JSON = "^0.20, ^0.21"
 JSON3 = "1.13.2"
 LazyArtifacts = "1.6"