fix: Update grcov installation and build/test commands (#1907)

# Goal
The goal of this PR is to move grcov to the `stable` channel.

# How to Test
- Read through changes and validate.
- [x] CI passed `Code Coverage` test [when a .rs file was edited]
https://github.com/LibertyDSNP/frequency/actions/runs/8148373324/job/22271097267

# Discussion
<!-- List discussion items -->

# Checklist
- [ ] Chain spec updated
- [ ] Custom RPC OR Runtime API added/changed? Updated js/api-augment.
- [ ] Design doc(s) updated
- [ ] Tests added
- [ ] Benchmarks added
- [ ] Weights updated

---------

Co-authored-by: Matthew Orris <--help>

.github/workflows/common/codecov/action.yml

@@ -9,18 +9,20 @@ runs:
   steps:
     - name: Install grcov
       shell: bash
-      run: cargo +nightly-2024-03-01 install --locked grcov
+      run: cargo install --locked grcov
     - name: Build
       shell: bash # Limited to 10 threads max
-      run: cargo +nightly-2024-03-01 build -j 10 --features frequency-lint-check
+      run: cargo build -j 10 --features frequency-lint-check
       env:
+        RUSTC_BOOTSTRAP: 1
         CARGO_INCREMENTAL: '0'
         RUSTFLAGS: "-Zprofile -Ccodegen-units=1 -Copt-level=0 -Clink-dead-code -Coverflow-checks=off -Zpanic_abort_tests -Cpanic=abort"
         RUSTDOCFLAGS: "-Cpanic=abort"
     - name: Test
       shell: bash # Limited to 10 threads max
-      run: cargo +nightly-2024-03-01 test -j 10 --features frequency-lint-check
+      run: cargo test -j 10 --features frequency-lint-check
       env:
+        RUSTC_BOOTSTRAP: 1
         CARGO_INCREMENTAL: '0'
         RUSTFLAGS: "-Zprofile -Ccodegen-units=1 -Copt-level=0 -Clink-dead-code -Coverflow-checks=off -Zpanic_abort_tests -Cpanic=abort"
         RUSTDOCFLAGS: "-Cpanic=abort"