ci: Fix avm tests

[acheroncrypto]

Problem

Reusable tests workflow runs avm tests twice, which sometimes causes the CI to fail due to GitHub rate-limits.

anchor/.github/workflows/reusable-tests.yaml

Lines 53 to 57 in 16e166c

	- run: cargo fmt -- --check
	- run: cargo clippy --all-targets -- -D warnings
	- run: cargo test
	# using singlethreaded testing for avm so that tests that change files do not conflict with each other
	- run: cd avm && cargo fmt -- --check && cargo clippy --all-targets -- -D warnings && cargo test -- --test-threads=1

As the comment suggests, this doesn't seem to be intent of the initial author.

Summary of changes

Exclude avm from the initial cargo test command, and run avm as single-threaded separately afterwards.

Additionally, remove the redundant formatting (cargo fmt) and linting (cargo clippy) commands specific to avm, since the initial runs already take care of this process.

[vercel]

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