fix: add missing raw string in REGEX_RULES (#3104)

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I ran into an error while trying to use the trim_galore/pe wrapper:
```
/path/to/project/.snakemake/scripts/tmph05pgi_u.wrapper.py:38: SyntaxWarning: invalid escape sequence '\.'
  REGEX_RULES = [r"\.fastq$", "\.fastq\.gz$", r"\.fq$", r"\.fq\.gz$"]
```

The fix for that issue was easy and obvious, I fixed the raw string for
`.fastq.gz` files in the list of regex patterns.

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bio/trim_galore/pe/wrapper.py

@@ -31,7 +31,7 @@ def fasta_filename(infile: str, infix: str, out_gzip: bool) -> str:
     """
     base_input = os.path.basename(infile)
     suffix = ".gz" if out_gzip or infile.endswith(".gz") else ""
-    REGEX_RULES = [r"\.fastq$", "\.fastq\.gz$", r"\.fq$", r"\.fq\.gz$"]
+    REGEX_RULES = [r"\.fastq$", r"\.fastq\.gz$", r"\.fq$", r"\.fq\.gz$"]
     for regex in REGEX_RULES:
         if re.search(regex, base_input):
             return re.sub(regex, f"{infix}.fq", base_input) + suffix