Allow actions-rs/grcov to fail

[atodorov]

because recently it started failing with:

Error: failed to compile grcov v0.8.19, intermediate artifacts can be found at /var/folders/h1/8hndypj13nsbj5pn4xsnv1tm0000gn/T/cargo-installyBLQUt
Caused by:
package clap_lex v0.7.0 cannot be built because it requires rustc 1.74 or newer, while the currently active rustc version is 1.72.0-nightly
Try re-running cargo install with --locked

and this actions doesn't allow control over how cargo install is executed internally

Description of proposed changes

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Practical tips for PR review & merge:

• All GitHub Actions report PASS
• Newly added code/functions have unit tests
  • Coverage tools report all newly added lines as covered
  • The positive scenario is exercised
  • Negative scenarios are exercised, e.g. assert on all possible errors
  • Assert on events triggered if applicable
  • Assert on changes made to storage if applicable
• Modified behavior/functions - try to make sure above test items are covered
• Integration tests are added if applicable/needed