CI: Set flaky [evm], [sc_rollup] tests as flaky

Context

Builds on !11174 (merged).

Adds the tag Ci.flaky to the tests below. The consequence of this (after !11174 (merged) ) is that they are not executed in normal before_merging pipelines, but are instead executed in scheduled pipelines with a higher retry count:

Alpha: arith - garbage collection is triggered and finishes correctly (full) (many_gc)
Alpha: arith - garbage collection is triggered and finishes correctly (full) (sparse_gc)
Alpha: wasm_2_0_0 - garbage collection is triggered and finishes correctly (full) (many_gc)
Alpha: wasm_2_0_0 - garbage collection is triggered and finishes correctly (full) (sparse_gc)
Nairobi->Alpha: wasm_2_0_0 - refutation games over migrations (inbox_proof_1_at_published_commitment)
Nairobi->Alpha: wasm_2_0_0 - refutation games over migrations (pvm_proof_2_at_inbox)
Nairobi->Alpha: wasm_2_0_0 - refutation games over migrations (pvm_proof_2_at_published_commitment)
Nairobi: arith - garbage collection is triggered and finishes correctly (full) (many_gc)
Nairobi: arith - garbage collection is triggered and finishes correctly (full) (sparse_gc)
Nairobi->Oxford: wasm_2_0_0 - refutation games over migrations (inbox_proof_1_at_published_commitment)
Nairobi->Oxford: wasm_2_0_0 - refutation games over migrations (pvm_proof_2_at_inbox)
Nairobi->Oxford: wasm_2_0_0 - refutation games over migrations (pvm_proof_2_at_published_commitment)
Nairobi: wasm_2_0_0 - garbage collection is triggered and finishes correctly (full) (many_gc)
Nairobi: wasm_2_0_0 - garbage collection is triggered and finishes correctly (full) (sparse_gc)
Oxford: arith - garbage collection is triggered and finishes correctly (full) (many_gc)
Oxford: arith - garbage collection is triggered and finishes correctly (full) (sparse_gc)
Oxford: wasm_2_0_0 - garbage collection is triggered and finishes correctly (full) (many_gc)
Oxford: wasm_2_0_0 - garbage collection is triggered and finishes correctly (full) (sparse_gc)

Manually testing the MR

Check that the list of new tests with the tag flaky are as specified above:

comm -1 -3  <(cd ../master; tezt_ --list-tsv flaky | grep -v qcheck | csvcut -t -c 2 | sort) <(tezt_ --list-tsv flaky | grep -v qcheck | csvcut -t -c 2 | sort)

with alias tezt_=_build/default/tezt/tests/main.exe.

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR