CI: fix coverage

[TriplEight]

• restores code coverage how it used to measure previously - with an old-style instrumentation (but with branch coverage)
• some chore

CC: #857
Closes: paritytech/ci_cd#160 #863 https://github.com/paritytech/ci_cd/issues/13

[TriplEight]

Note: #863 (review)

[codecov-commenter]

Codecov Report

Merging #895 (de0277b) into master (5571724) will increase coverage by 1.26%.
The diff coverage is 81.80%.

@@            Coverage Diff             @@
##           master     #895      +/-   ##
==========================================
+ Coverage   83.33%   84.59%   +1.26%     
==========================================
  Files         163      172       +9     
  Lines        7502     7960     +458     
==========================================
+ Hits         6252     6734     +482     
+ Misses       1250     1226      -24     

Impacted Files	Coverage Δ
crates/env/src/api.rs	50.00% <0.00%> (+6.25%)	⬆️
crates/env/src/backend.rs	0.00% <ø> (ø)
...tes/env/src/engine/experimental_off_chain/types.rs	0.00% <0.00%> (ø)
crates/env/src/engine/off_chain/db/accounts.rs	86.90% <ø> (ø)
crates/env/src/engine/off_chain/db/block.rs	100.00% <ø> (ø)
crates/env/src/engine/off_chain/impls.rs	56.33% <0.00%> (+3.70%)	⬆️
crates/env/src/engine/off_chain/test_api.rs	80.85% <0.00%> (ø)
crates/env/src/engine/off_chain/typed_encoded.rs	80.48% <ø> (ø)
crates/env/src/types.rs	44.44% <ø> (ø)
crates/lang/codegen/src/generator/cross_calling.rs	94.82% <ø> (ø)
... and 98 more

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[TriplEight]

Feel free to merge if you're OK to do without -Clink-dead-code .

[HCastano]

Feel free to merge if you're OK to do without -Clink-dead-code .

I'm hesitant to merge without this since Robin mentioned that having this flag was correct. Does the Codecov job not pass if this flag is enabled, or what happens?

[TriplEight]

Shish, I thought it already works for a month. It could have worked at least somehow. The job breaks with this flag.

[cmichi]

I'll merge in the current state and create create a follow-up adding the -Clink-dead-code flag and a fix for the error it causes.