Ci mamba fix

[Vipul-Cariappa]

Builds on top of #2758

[Vipul-Cariappa]

@certik, as I can't write to that branch, I will be using this branch.

[Vipul-Cariappa]

I had to skip the test_bit_length integration test from llvm and llvm_jit. I have commented about it on an issue related to bit_length. see #1836 (comment).

[Vipul-Cariappa]

@certik, this might be a simpler fix than #2758.
Only had to skip test_bit_length integrations test, compared to skipping both test_llvm and the integration test.
And we need not pin every single package. I have only pined the necessary packages, and most probably conda will install the newest available versions of the other packages.

[certik]

Fixed in #2764.