GH-43548: [R][CI] Use grep -F to simplify matching or rchk output (#4…

…3477)

Passing along a minor change we made in our own mimeo of this GHA.

Resolves #43548
* GitHub Issue: #43548

Authored-by: Michael Chirico <chiricom@google.com>
Signed-off-by: Jonathan Keane <jkeane@gmail.com>

dev/tasks/r/github.linux.rchk.yml

@@ -54,7 +54,7 @@ jobs:
         # ERROR: too many states (abstraction error?))
         # https://github.com/kalibera/rchk
         run: |
-          if [ $(grep -c "Suspicious call" rchk.out) -gt 0 ] || [ $(grep -c "\[UP\]" rchk.out) -gt 0 ] || [ $(grep -c "\[PB\]" rchk.out) -gt 0 ]; then
+          if [ $(grep -Fc "Suspicious call" rchk.out) -gt 0 ] || [ $(grep -Fc "[UP]" rchk.out) -gt 0 ] || [ $(grep -Fc "[PB]" rchk.out) -gt 0 ]; then
             echo "Found rchk errors"
             cat rchk.out
             exit 1