Mathicgb crash/assertion failure with Groebner bases

While messing around with the failures in #1742, I got a crash from the assertion at `e/mathicgb/mathicgb/F4MatrixBuilder2.cpp:133`. In particular, I have the following stack trace (only the interesting elements)

```
#1 0x00007ffff5ef9862 in abort () from /usr/lib/libc.so.6
#2 0x00007ffff5ef9747 in __assert_fail_base.cold () from /usr/lib/libc.so.6
#3 0x00007ffff5f08616 in __assert_fail () from /usr/lib/libc.so.6
#4 0x000055555614cb98 in mgb::F4MatrixBuilder2::Builder::initializeRowsToReduce (this=0x7fffe7f58660,
tasks=std::vector of length 79, capacity 128 = {...})
at /home/jay/repos/M2-clean/M2/Macaulay2/e/mathicgb/mathicgb/F4MatrixBuilder2.cpp:133
#5 0x000055555614d444 in mgb::F4MatrixBuilder2::Builder::buildMatrixAndClear (this=0x7fffe7f58660,
tasks=std::vector of length 79, capacity 128 = {...}, quadMatrix=...)
at /home/jay/repos/M2-clean/M2/Macaulay2/e/mathicgb/mathicgb/F4MatrixBuilder2.cpp:148
#6 0x000055555614c1b6 in mgb::F4MatrixBuilder2::buildMatrixAndClear (this=0x7fffe7f58860,
quadMatrix=...) at /home/jay/repos/M2-clean/M2/Macaulay2/e/mathicgb/mathicgb/F4MatrixBuilder2.cpp:587
#7 0x000055555611ef5a in mgb::F4Reducer::classicReduceSPolySet (this=0x7fffd81ba800,
spairs=std::vector of length 51, capacity 64 = {...}, basis=...,
reducedOut=std::vector of length 0, capacity 0)
at /home/jay/repos/M2-clean/M2/Macaulay2/e/mathicgb/mathicgb/F4Reducer.cpp:205
#8 0x00005555560312b1 in mgb::ClassicGBAlg::step (this=0x7fffe7f58e30)
at /home/jay/repos/M2-clean/M2/Macaulay2/e/mathicgb/mathicgb/ClassicGBAlg.cpp:374
#9 0x0000555556030c17 in mgb::ClassicGBAlg::computeGrobnerBasis (this=0x7fffe7f58e30)
at /home/jay/repos/M2-clean/M2/Macaulay2/e/mathicgb/mathicgb/ClassicGBAlg.cpp:324
#10 0x00005555560333d3 in mgb::computeGBClassicAlg (inputBasis=..., params=...)
at /home/jay/repos/M2-clean/M2/Macaulay2/e/mathicgb/mathicgb/ClassicGBAlg.cpp:679
#11 0x0000555556022088 in mgb::mgbi::internalComputeGroebnerBasis (inputWhichWillBeCleared=...,
output=...) at /home/jay/repos/M2-clean/M2/Macaulay2/e/mathicgb/mathicgb.cpp:976
#12 0x0000555555871c4d in mgb::computeGroebnerBasis (inputWhichWillBeCleared=...,
output=...) at /home/jay/repos/M2-clean/M2/Macaulay2/e/mathicgb/mathicgb.h:913
#13 0x000055555586de3b in rawMGB (inputMatrix=0x7fffd3e05720, reducer=1, spairGroupSize=0, nthreads=0,
logging=0x7fffeaa15080) at /home/jay/repos/M2-clean/M2/Macaulay2/e/interface/groebner.cpp:810
```

Originally,I got this crash running code from SpecialFanoFourfolds, but via the debugger I managed to extract the following example: [test2.m2.txt](https://github.com/Macaulay2/M2/files/7480862/test2.m2.txt).

This extracted test case is crashing most of the time for me (running it via load), although not 100% of the time, which makes me think it's a race condition and or memory corruption.

Also, I don't know if #2162 is related, but this isn't on the same platforms. I'm on amd64.